image-source: Do not change blend state

The blend state does not need to (and should not) be changed.  This
fixes an issue where if filters are applied to an image source, the
image source will paint incorrectly.

plugins/image-source/image-source.c

@@ -151,7 +151,6 @@ static void image_source_render(void *data, gs_effect_t *effect)
 	if (!context->image.texture)
 		return;
 
-	gs_reset_blend_state();
 	gs_effect_set_texture(gs_effect_get_param_by_name(effect, "image"),
 			context->image.texture);
 	gs_draw_sprite(context->image.texture, 0,