fix(fuse): end a mirror pass at the stop (B169)

A stop that came while a mirror pass was uploading let the pass go on to
the next level of folders until the stop gave up on it and the runtime's
end cancelled the uploads under it. Once the daemon is stopping, a batch
starts none of its waiting ops, lets the ones sending finish, and ends
the pass; the remote walk and a new pass stop too.

docs/CHANGELOG.md

@@ -66,6 +66,8 @@ by its local id, in the queue, the stored tree and pins alike.
   took close to 2 s with 37,000 files at every start (B167).
 - **Files deleted with their folder while uploading stay deleted.** The mount no longer tries
   to upload them to the top of your Drive instead (B168).
+- **Stopping the daemon during a folder sync no longer waits for the sync.** The uploads in
+  progress finish, and the rest waits for the next start (B169).
 - **A file renamed just as its upload finished keeps its new name.** The mount no longer showed
   the old name, and a second rename no longer failed with "No such file or directory" (B152).
 - **A change that waits for a name to be freed no longer waits seconds after it is.** A rename or