DrawManager: OpenGL State Image Rendering

The OpenGL state was not set to blender defaults when using
`DRW_render_to_image` path. This is only used when doing F12-rendering.
Cause of changes with the `RESTART_INDEX` hair rendering was rendering
the restart_index as an actual vertex index.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D5039

source/blender/draw/intern/draw_manager.c

@@ -2001,6 +2001,8 @@ void DRW_render_to_image(RenderEngine *engine, struct Depsgraph *depsgraph)
 
   /* Reset state before drawing */
   DRW_state_reset();
+  /* Set the default Blender draw state */
+  GPU_state_init();
 
   /* Init render result. */
   RenderResult *render_result = RE_engine_begin_result(engine,