check if ctx->Driver.GetBufferSize==NULL and no-op

src/mesa/main/buffers.c

@@ -604,6 +604,10 @@ void _mesa_resizebuffers( GLcontext *ctx )
    if (MESA_VERBOSE & VERBOSE_API)
       _mesa_debug(ctx, "glResizeBuffersMESA\n");
 
+   if (!ctx->Driver.GetBufferSize) {
+      return;
+   }
+
    if (ctx->WinSysDrawBuffer) {
       GLuint newWidth, newHeight;
       GLframebuffer *buffer = ctx->WinSysDrawBuffer;

src/mesa/main/context.c

@@ -1629,11 +1629,12 @@ static void
 initialize_framebuffer_size(GLcontext *ctx, GLframebuffer *fb)
 {
    GLuint width, height;
-   ASSERT(ctx->Driver.GetBufferSize);
-   ctx->Driver.GetBufferSize(fb, &width, &height);
-   if (ctx->Driver.ResizeBuffers)
-      ctx->Driver.ResizeBuffers(ctx, fb, width, height);
-   fb->Initialized = GL_TRUE;
+   if (ctx->Driver.GetBufferSize) {
+      ctx->Driver.GetBufferSize(fb, &width, &height);
+      if (ctx->Driver.ResizeBuffers)
+         ctx->Driver.ResizeBuffers(ctx, fb, width, height);
+      fb->Initialized = GL_TRUE;
+   }
 }