gallium: check if surface has defined status in check_clear_depth_with_quad()

This was part of Keith's patch from Friday.

src/mesa/state_tracker/st_cb_clear.c

@@ -408,7 +408,9 @@ check_clear_depth_with_quad(GLcontext *ctx, struct gl_renderbuffer *rb)
    const struct st_renderbuffer *strb = st_renderbuffer(rb);
    const GLboolean isDS = is_depth_stencil_format(strb->surface->format);
    return  ctx->Scissor.Enabled
-      || (isDS && ctx->DrawBuffer->Visual.stencilBits > 0);
+      || (isDS && 
+	  strb->surface->status == PIPE_SURFACE_STATUS_DEFINED &&
+	  ctx->DrawBuffer->Visual.stencilBits > 0);
 }