[OpenGL backend] Add fallback for if glGenerateMipmap is unavailable

[past-due]

We have reports that certain (older) Intel graphics drivers may not provide glGenerateMipmap support on Windows (in certain situations).

Provide a fallback path for when glGenerateMipmap is unavailable.

[past-due]

Player confirmed (on IRC) that this fixed their issues.

For reference, here is a log showing the error in 3.3.0_beta1:

Expand log

-------------------
 
Error occurred on Monday, March 11, 2019 at 13:47:15.
 
Program: C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe (warzone2100)
Command line: "C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe"
Version: Version: 3.3.0-beta1, Built: Feb 10 2019
Distributor: wz2100.net
Compiled on: Feb 10 2019 21:03:39
Compiled by: MSVC 191627025 (c++ std: 201402)
Compiled mode: Release build
Executed on: Mon Mar 11 13:47:07 2019
Operating system: Windows
Version: 6.1.7601.24354
Machine: x86_64
 
Pointers: 32bit
 
Compiled against PhysicsFS version: 3.0.1
Running with PhysicsFS version: 3.0.1
 
Misc Data:
[13:47:08]Video Mode 640 x 480 (fullscreen)
[13:47:08]OpenGL Vendor: Intel
[13:47:08]OpenGL Renderer: Mobile Intel(R) 4 Series Express Chipset Family
[13:47:08]OpenGL Version: 2.1.0 - Build 8.15.10.2302
[13:47:08]GLEW Version: 2.1.0
[13:47:08]OpenGL GLSL Version : 1.20  - Intel Build 8.15.10.2302
[13:47:09]OpenAL Device Name: OpenAL Soft
[13:47:09]OpenAL Vendor: OpenAL Community
[13:47:09]OpenAL Version: 1.1 ALSOFT 1.19.1
[13:47:09]OpenAL Renderer: OpenAL Soft
[13:47:09]OpenAL Extensions: AL_EXT_ALAW AL_EXT_BFORMAT AL_EXT_DOUBLE AL_EXT_EXPONENT_DISTANCE AL_EXT_FLOAT32 AL_EXT_IMA4 AL_EXT_LINEAR_DISTANCE AL_EXT_MCFORMATS AL_EXT_MULAW AL_EXT_MULAW_BFORMAT AL_EXT_MULAW_MCFORMATS AL_EXT_OFFSET AL_EXT_source_distance_model AL_EXT_SOURCE_RADIUS AL_EXT_STEREO_ANGLES AL_LOKI_quadriphonic AL_SOFT_block_alignment AL_SOFT_deferred_updates AL_SOFT_direct_channels AL_SOFTX_events AL_SOFTX_filter_gain_ex AL_SOFT_gain_clamp_ex AL_SOFT_loop_points AL_SOFTX_map_buffer AL_SOFT_MSADPCM AL_SO
[13:47:09]Using Backend: SDL
[13:47:09]Using language: System locale
 
 
C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe caused an Access Violation at location 00000000 Writing to location 00000000.
 
 
Registers:
eax=00000000 ebx=003fdf1c ecx=0569d7f0 edx=00000027 esi=00000220 edi=00000008
eip=00000000 esp=003fde58 ebp=003fdef8 iopl=0         nv up ei pl nz na po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010206

<snip>

Call Stack:
0138733E  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  gl_texture::generate_mip_levels  c:\projects\warzone2100\lib\ivis_opengl\gfx_api_gl.cpp:102
01386626  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  pie_AddTexPage  c:\projects\warzone2100\lib\ivis_opengl\tex.cpp:121
01386255  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  iV_GetTexture  c:\projects\warzone2100\lib\ivis_opengl\tex.cpp:224
013851A8  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  iV_ProcessIMD  c:\projects\warzone2100\lib\ivis_opengl\imdload.cpp:1012
01385DAD  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  tryLoad  c:\projects\warzone2100\lib\ivis_opengl\imdload.cpp:80
013857CB  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  modelGet  c:\projects\warzone2100\lib\ivis_opengl\imdload.cpp:110
0133EA8F  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  statsGetIMD  c:\projects\warzone2100\src\stats.cpp:259
0133D3DD  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  loadWeaponStats  c:\projects\warzone2100\src\stats.cpp:409
011DDD2C  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  bufferSWEAPONLoad  c:\projects\warzone2100\src\data.cpp:175
013CAA12  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  resLoadFile  c:\projects\warzone2100\lib\framework\frameresource.cpp:547
013CD401  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  res_parse  c:\projects\warzone2100\build\lib\framework\resource_parser.ypp:119
013CA3F5  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  resLoad  c:\projects\warzone2100\lib\framework\frameresource.cpp:206
01296417  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  startMultiplayerGame  c:\projects\warzone2100\src\multiint.cpp:3487
01292EB7  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  processMultiopWidgets  c:\projects\warzone2100\src\multiint.cpp:3379
01294DF7  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  runMultiOptions  c:\projects\warzone2100\src\multiint.cpp:3896
013608C4  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  titleLoop  c:\projects\warzone2100\src\wrappers.cpp:183
0126CFBD  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  runTitleLoop  c:\projects\warzone2100\src\main.cpp:981
0126BF62  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  mainLoop  c:\projects\warzone2100\src\main.cpp:1058
013B14CB  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  wzMainEventLoop  c:\projects\warzone2100\lib\sdl\main_sdl.cpp:2274
0126CEEE  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  realmain  c:\projects\warzone2100\src\main.cpp:1393
013EC3DE  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  main_getcmdline  c:\projects\warzone2100\vcpkg\buildtrees\sdl2\src\ease-2.0.9-ad425106c1\src\main\windows\sdl_windows_main.c:177
013EC325  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  WinMain  c:\projects\warzone2100\vcpkg\buildtrees\sdl2\src\ease-2.0.9-ad425106c1\src\main\windows\sdl_windows_main.c:205
013EB804  C:\Program Files (x86)\Warzone 2100-3.3.0-beta1\bin\warzone2100.exe  __scrt_common_main_seh  d:\agent\_work\2\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288
76BA343D  C:\Windows\syswow64\kernel32.dll:76BA343D  BaseThreadInitThunk
777F9802  C:\Windows\SysWOW64\ntdll.dll:777F9802  RtlInitializeExceptionChain
777F97D5  C:\Windows\SysWOW64\ntdll.dll:777F97D5  RtlInitializeExceptionChain