fix error when create backbuffer with msaa and srgb format (#2258)
fix error when create backbuffer with msaa and srgb format (#2258)


LWJGL-CI/bgfx,jdryg/bgfx,mendsley/bgfx,bkaradzic/bgfx,mendsley/bgfx,LWJGL-CI/bgfx,jdryg/bgfx,jdryg/bgfx,bkaradzic/bgfx,jdryg/bgfx,LWJGL-CI/bgfx,emoon/bgfx,bkaradzic/bgfx,bkaradzic/bgfx,LWJGL-CI/bgfx,mendsley/bgfx,emoon/bgfx,emoon/bgfx