anv/image: Return early when unbinding an image

Found by inspection.

Reviewed-by: Chad Versace <chadversary@chromium.org>
 Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Cc: "17.0 13.0" <mesa-stable@lists.freedesktop.org>

(cherry picked from commit c942faf8f37d14e7934a21c15ad2438dde2d501e)
diff --git a/src/intel/vulkan/anv_image.c b/src/intel/vulkan/anv_image.c
index 034635c..a3e3a09 100644
--- a/src/intel/vulkan/anv_image.c
+++ b/src/intel/vulkan/anv_image.c
@@ -346,14 +346,15 @@
    ANV_FROM_HANDLE(anv_device_memory, mem, _memory);
    ANV_FROM_HANDLE(anv_image, image, _image);
 
-   if (mem) {
-      image->bo = &mem->bo;
-      image->offset = memoryOffset;
-   } else {
+   if (mem == NULL) {
       image->bo = NULL;
       image->offset = 0;
+      return VK_SUCCESS;
    }
 
+   image->bo = &mem->bo;
+   image->offset = memoryOffset;
+
    if (image->aux_surface.isl.size > 0) {
 
       /* The offset and size must be a multiple of 4K or else the