file-operations: reset skipped status of files on copy/move

When copying or moving a file, the file’s “skipped” status is not reset,
resulting in cases where the code starts skipping all files. In such
cases the progress popover will show the finished operation count higher
than the total amount of files.

https://bugzilla.gnome.org/show_bug.cgi?id=779569

src/nautilus-file-operations.c

@@ -5168,6 +5168,8 @@ copy_move_file (CopyMoveJob   *copy_job,
 
     job = (CommonJob *) copy_job;
 
+    *skipped_file = FALSE;
+
     if (should_skip_file (job, src))
     {
         *skipped_file = TRUE;