vo_gpu: opengl: make sure to always clean up debug callbacks

In theory this mostly happens automatically, especially after the 5
vsync limit disables this already. But if we uninit before 5 vsyncs are
rendered, this can get left in a dangling 'enabled' state, which leaks a
debug report callback.

Always explicitly disable it just to be on the safe side.

video/out/opengl/context.c

@@ -135,6 +135,10 @@ void ra_gl_ctx_uninit(struct ra_ctx *ctx)
         ctx->swapchain = NULL;
     }
 
+    // Clean up any potentially left-over debug callback
+    if (ctx->ra)
+        ra_gl_set_debug(ctx->ra, false);
+
     ra_free(&ctx->ra);
 }