Fix hangs on QFileSystemWatcher.

QFileSystemWatcher hangs at a mutex or semaphore when adding network
paths on OS X system.

There is an else block that does not increment the 'it' iterator
with ++it; inside the QFseventsFileSystemWatcherEngine::checkDir() call.

Change-Id: I6c250c7f3d25399c3a0a58ce864e9466320b166b
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>

src/corelib/io/qfilesystemwatcher_fsevents.mm

@@ -149,6 +149,7 @@ bool QFseventsFileSystemWatcherEngine::checkDir(DirsByName::iterator &it)
         }
         if (dirChanged)
             emit emitDirectoryChanged(info.origPath, false);
+        ++it;
     }
 
     return needsRestart;