Shutdown GitStatusCache before components it depends on

Tweak the order that components are shutdown, to shutdown the
GitStatusCache before other components that it depends on. This is to
prevent problems that might arise from a component being disabled that
GitStatusCache depends on.

GVFS/GVFS.Virtualization/FileSystemCallbacks.cs

@@ -196,8 +196,11 @@ public void Stop()
                 this.postFetchJobThread?.Abort();
             }
 
-            this.fileSystemVirtualizer.PrepareToStop();
+            // Shutdown the GitStatusCache before other
+            // components that it depends on.
             this.gitStatusCache.Shutdown();
+
+            this.fileSystemVirtualizer.PrepareToStop();
             this.backgroundFileSystemTaskRunner.Shutdown();
             this.GitIndexProjection.Shutdown();
             this.BlobSizes.Shutdown();