[fix JENKINS-20531], catch GitException during fetch, throw AbortExce…

…ption

The AbortException is already thrown from another area of the same
method, so throwing the AbortException is likely no worse than the
existing AbortException which is thrown (instead of GitException).

src/main/java/hudson/plugins/git/GitSCM.java

@@ -921,7 +921,12 @@ private void retrieveChanges(Run build, GitClient git, TaskListener listener) th
         }
 
         for (RemoteConfig remoteRepository : repos) {
-            fetchFrom(git, listener, remoteRepository);
+            try {
+                fetchFrom(git, listener, remoteRepository);
+            } catch (GitException ex) {
+                ex.printStackTrace(listener.error("Error fetching changes from repo '%s'", remoteRepository.getName()));
+                throw new AbortException();
+            }
         }
     }