Fix T46496: GL Render fails w/ Anti-Aliasing

Needed to check if scaled-multisample-blit is supported.

source/blender/gpu/intern/gpu_extensions.c

@@ -1455,7 +1455,10 @@ GPUOffScreen *GPU_offscreen_create(int width, int height, int samples, char err_
 		    /* Only needed for GPU_offscreen_read_pixels.
 		     * We could add an arg if we intend to use multi-samle
 		     * offscreen buffers w/o reading their pixels */
-		    !GLEW_EXT_framebuffer_blit)
+		    !GLEW_EXT_framebuffer_blit ||
+		    /* This is required when blitting from a multi-sampled buffers,
+		     * even though we're not scaling. */
+		    !GLEW_EXT_framebuffer_multisample_blit_scaled)
 		{
 			samples = 0;
 		}