Initialize member variables in MythRenderOpenGL ctor

The refactor of the OpenGL code appears to result
in the ResetVars and ResetProcs functions being
called from the ctors of MythRenderOpenGL[12], but
invoke them explicitly to keep Coverity happy.

Fixes Coverity 700926 and 700927

Fixes #11660.

Signed-off-by: Paul Harrison <pharrison@mythtv.org>

mythtv/libs/libmythui/mythrender_opengl.cpp

@@ -106,11 +106,15 @@ MythRenderOpenGL::MythRenderOpenGL(const QGLFormat& format, QPaintDevice* device
                                    RenderType type)
   : QGLContext(format, device), MythRender(type)
 {
+    ResetVars();
+    ResetProcs();
 }
 
 MythRenderOpenGL::MythRenderOpenGL(const QGLFormat& format, RenderType type)
   : QGLContext(format), MythRender(type)
 {
+    ResetVars();
+    ResetProcs();
 }
 
 MythRenderOpenGL::~MythRenderOpenGL()