gpu: validate transfer buffer usage (#15923)

src/gpu/SDL_gpu.c

@@ -1430,6 +1430,13 @@ SDL_GPUTransferBuffer *SDL_CreateGPUTransferBuffer(
         return NULL;
     }
 
+    if (device->debug_mode) {
+        if (createinfo->usage != SDL_GPU_TRANSFERBUFFERUSAGE_UPLOAD &&
+            createinfo->usage != SDL_GPU_TRANSFERBUFFERUSAGE_DOWNLOAD) {
+            SDL_assert_release(!"Invalid transfer buffer usage!");
+        }
+    }
+
     const char *debugName = SDL_GetStringProperty(createinfo->props, SDL_PROP_GPU_TRANSFERBUFFER_CREATE_NAME_STRING, NULL);
 
     return device->CreateTransferBuffer(