message: Fix warning on setting uniform for image
  When selecting "Quad Overdraw (Pass)" from the texture viewer, I get this warning :
  Log     - Got a Debug message from GL_DEBUG_SOURCE_API, type GL_DEBUG_TYPE_ERROR, ID 81, severity GL_DEBUG_SEVERITY_HIGH:
  'GL_INVALID_OPERATION in glUniform1("overdrawImage"@12 is image, not uint)'
diff: @@ -1344,7 +1344,7 @@ ResourceId GLReplay::RenderOverlay(ResourceId texid, CompType typeHint, DebugOve
  GLint loc = drv.glGetUniformLocation(DebugData.overlayProg, "overdrawImage");
  if(loc != -1)
  - drv.glUniform1ui(loc, 0);
  + drv.glUniform1i(loc, 0);
  else
  RDCERR("Couldn't get location of overdrawImage");
  