wined3d: Check the writemask for the correct render target in draw_primitive().

dlls/wined3d/context.c

@@ -5105,6 +5105,15 @@ static GLenum gl_tfb_primitive_type_from_d3d(enum wined3d_primitive_type primiti
     }
 }
 
+static unsigned int get_render_target_writemask(const struct wined3d_blend_state *state, unsigned int index)
+{
+    if (!state)
+        return 0xf;
+    if (!state->desc.independent)
+        index = 0;
+    return state->desc.rt[index].writemask;
+}
+
 /* Routine common to the draw primitive and draw indexed primitive routines */
 void draw_primitive(struct wined3d_device *device, const struct wined3d_state *state,
         const struct wined3d_draw_parameters *parameters)
@@ -5154,7 +5163,7 @@ void draw_primitive(struct wined3d_device *device, const struct wined3d_state *s
         if (!(rtv = fb->render_targets[i]) || rtv->format->id == WINED3DFMT_NULL)
             continue;
 
-        if (!state->blend_state || state->blend_state->desc.rt[0].writemask)
+        if (get_render_target_writemask(state->blend_state, i))
         {
             wined3d_rendertarget_view_load_location(rtv, context, rtv->resource->draw_binding);
             wined3d_rendertarget_view_invalidate_location(rtv, ~rtv->resource->draw_binding);