Fix `--no-overwrite` for playlist infojson

Fixes: https://github.com/yt-dlp/yt-dlp/issues/1467#issuecomment-1079922971

yt_dlp/YoutubeDL.py

@@ -1815,7 +1815,7 @@ class YoutubeDL(object):
         ie_result['entries'] = playlist_results
 
         # Write the updated info to json
-        if _infojson_written and self._write_info_json(
+        if _infojson_written is True and self._write_info_json(
                 'updated playlist', ie_result,
                 self.prepare_filename(ie_copy, 'pl_infojson'), overwrite=True) is None:
             return
@@ -3786,7 +3786,7 @@ class YoutubeDL(object):
         return encoding
 
     def _write_info_json(self, label, ie_result, infofn, overwrite=None):
-        ''' Write infojson and returns True = written, False = skip, None = error '''
+        ''' Write infojson and returns True = written, 'exists' = Already exists, False = skip, None = error '''
         if overwrite is None:
             overwrite = self.params.get('overwrites', True)
         if not self.params.get('writeinfojson'):
@@ -3798,14 +3798,15 @@ class YoutubeDL(object):
             return None
         elif not overwrite and os.path.exists(infofn):
             self.to_screen(f'[info] {label.title()} metadata is already present')
-        else:
-            self.to_screen(f'[info] Writing {label} metadata as JSON to: {infofn}')
-            try:
-                write_json_file(self.sanitize_info(ie_result, self.params.get('clean_infojson', True)), infofn)
-            except (OSError, IOError):
-                self.report_error(f'Cannot write {label} metadata to JSON file {infofn}')
-                return None
-        return True
+            return 'exists'
+
+        self.to_screen(f'[info] Writing {label} metadata as JSON to: {infofn}')
+        try:
+            write_json_file(self.sanitize_info(ie_result, self.params.get('clean_infojson', True)), infofn)
+            return True
+        except (OSError, IOError):
+            self.report_error(f'Cannot write {label} metadata to JSON file {infofn}')
+            return None
 
     def _write_description(self, label, ie_result, descfn):
         ''' Write description and returns True = written, False = skip, None = error '''