[extractor/dropbox] Extract the correct `mountComponent`

yt_dlp/extractor/dropbox.py

@@ -53,8 +53,8 @@ class DropboxIE(InfoExtractor):
             else:
                 raise ExtractorError('Password protected video, use --video-password <password>', expected=True)
 
-        json_string = self._html_search_regex(r'InitReact\.mountComponent\(.*?,\s*(\{.+\})\s*?\)', webpage, 'Info JSON')
-        info_json = self._parse_json(json_string, video_id).get('props')
+        info_json = self._search_json(r'InitReact\.mountComponent\(.*?,', webpage, 'mountComponent', video_id,
+                                      contains_pattern=r'.+?"preview".+?', end_pattern=r'\)')['props']
         transcode_url = traverse_obj(info_json, ((None, 'preview'), 'file', 'preview', 'content', 'transcode_url'), get_all=False)
         formats, subtitles = self._extract_m3u8_formats_and_subtitles(transcode_url, video_id)