zink: Return early if the file descriptor could not have been duplicated/acquired

Do not continue and call drmIoctl on an invalid file descriptor.

Fix defect reported by Coverity Scan.

Argument cannot be negative

The negative argument will be interpreted as a very large unsigned value.

CID: 1544377
Cc: mesa-stable
Signed-off-by: Corentin Noël <corentin.noel@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27788>

src/gallium/drivers/zink/zink_screen.c

@@ -2367,7 +2367,7 @@ zink_screen_export_dmabuf_semaphore(struct zink_screen *screen, struct zink_reso
       .fd = -1,
    };
 
-   int fd;
+   int fd = -1;
    if (res->obj->is_aux) {
       fd = os_dupfd_cloexec(res->obj->handle);
    } else {
@@ -2378,6 +2378,11 @@ zink_screen_export_dmabuf_semaphore(struct zink_screen *screen, struct zink_reso
       VKSCR(GetMemoryFdKHR)(screen->dev, &fd_info, &fd);
    }
 
+   if (unlikely(fd < 0)) {
+      mesa_loge("MESA: Unable to get a valid memory fd");
+      return VK_NULL_HANDLE;
+   }
+
    int ret = drmIoctl(fd, DMA_BUF_IOCTL_EXPORT_SYNC_FILE, &export);
    if (ret) {
       if (errno == ENOTTY || errno == EBADF || errno == ENOSYS) {