if the module heap is >0 and <0x800 set it to 0x800

[cracyc]

ntvdm seems to work this way
fixes #615

[otya128]

It seems to behave differently when pSeg->minsize + pModule->ne_stack + pModule->ne_heap=0x800 exceeds 0x10000.

minsize:656 + stack:64622 + heap:19
---------------------------
Can't run 16-bit Windows program
---------------------------
Insufficient memory to run this application. Quit one or more Windows applications and then try again.
---------------------------
OK   
---------------------------

minsize:656 + stack:64621 + heap:19
ne_heap=256

minsize:656 + stack:62830 + heap:19
---------------------------
Can't run 16-bit Windows program
---------------------------
Insufficient memory to run this application. Quit one or more Windows applications and then try again.
---------------------------
OK   
---------------------------

minsize:656 + stack:62829 + heap:19
ne_heap=2048

minsize:656 + stack:62839 + heap:2039
---------------------------
Can't run 16-bit Windows program
---------------------------
Insufficient memory to run this application. Quit one or more Windows applications and then try again.
---------------------------
OK   
---------------------------

minsize:656 + stack:62838 + heap:2039
ne_heap=2039