SyncEngine: fix inode after move if the file has moved on the file system

This is the fix for issue #4370

Step to reproduce the bug:
 1) have lots of files in directory "dir1"
 2) do mkdir dir2 && mv dir1/* dir2
 3) DURING the sync (which takes time because of the many moves) do mkdir dir3 && mv dir2/* dir3/
 4) observe that files are PUT in the next sync

The problem is that SyncJournalFileRecord::SyncJournalFileRecord will fail to
get the inode after the forst move because the files are already moved on the
filesystem.  Normaly it should use the inode from the discovery phase in that
case but that is not working because it comes from the remote node in case of
moves, so the code in SyncEngine::treewalkFile would not set the inode.

Test in https://github.com/owncloud/smashbox/pull/143

src/libsync/syncengine.cpp

@@ -451,7 +451,7 @@ int SyncEngine::treewalkFile( TREE_WALK_FILE *file, bool remote )
     }
     item->_size = file->size;
 
-    if (!remote) {
+    if (!item->_inode) {
         item->_inode = file->inode;
     }