Fix T50051: Avoid crash when render grease pencil from VSE

The renderpasses for grease pencil are not necessary when render from
sequencer.

This fix solves the GPF but we need to rethink the complete render
process for grease pencil and integrate better in the render and
composition workflow.

Thanks to Dalai Felinto por helping in the debug and fixing of the
problem.

source/blender/editors/render/render_opengl.c

@@ -552,8 +552,11 @@ static void screen_opengl_render_apply(OGLRender *oglrender)
 		BLI_assert(view_id < oglrender->views_len);
 		RE_SetActiveRenderView(oglrender->re, rv->name);
 		oglrender->view_id = view_id;
-		/* add grease pencil passes */
-		add_gpencil_renderpass(oglrender, rr, rv);
+		/* add grease pencil passes. For sequencer, the render does not include renderpasses
+		 * TODO: The sequencer render of grease pencil should be rethought */
+		if (!oglrender->is_sequencer) {
+			add_gpencil_renderpass(oglrender, rr, rv);
+		}
 		/* render composite */
 		screen_opengl_render_doit(oglrender, rr);
 	}