FileURLDirectoryLoader should stop listing on connection errors

If FileURLDirectoryLoader has a net::DirectoryLister instance running,
it continues to call MaybeTransferPendingData() until the listing
finishes. If a connection error happens on the mojo interface, it
results in resetting |data_producer_|, and it causes a null pointer
dereference.

This issue was introduced after the last branch-cut. So only m78 is
affected.

Bug: 990579
Change-Id: I58f73d59022f89c82409e5fc10a6cb2a419b94d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1735241Reviewed-by: Chris Mumford <cmumford@google.com>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684288}

content/browser/file_url_loader_factory.cc

@@ -226,6 +226,7 @@ class FileURLDirectoryLoader
   }
 
   void OnConnectionError() {
+    lister_.reset();
     data_producer_.reset();
     binding_.Close();
     client_.reset();