Fixed imgui_impl_opengl3 broken in previous few commits. (#2591, #2593, #2594)
Fixed imgui_impl_opengl3 broken in previous few commits. (#2591, #2593, #2594)

ocornut/imgui,aimotive/imgui-glfw,cmaughan/imgui,ggtucker/imgui,burningreggae/imgui,bkaradzic/imgui,ggtucker/imgui,nProtect/imgui,dougbinks/imgui,aimotive/imgui-glfw,burningreggae/imgui,ggtucker/imgui,Flix01/imgui,cmaughan/imgui,Flix01/imgui,cmaughan/imgui,bkaradzic/imgui,ocornut/imgui,Flix01/imgui,cmaughan/imgui,nProtect/imgui,ocornut/imgui,nProtect/imgui,bkaradzic/imgui,dougbinks/imgui