Fix no text but only \n in xml, eg: uwIHyLPBZkY.

fetchYoutubeSubtitle.py

@@ -215,6 +215,13 @@ def float_to_srt_time_format(d: float) -> str:
     return time_fmt + ms
 
 
+def is_spaces_only(variable):
+    for char in variable:
+        if not char.isspace():
+            return False
+    return True
+
+
 def xml_caption_to_srt(xml_captions: str) -> str:
     """Convert xml caption tracks to "SubRip Subtitle (srt)".
     :param str xml_captions:
@@ -227,7 +234,7 @@ def xml_caption_to_srt(xml_captions: str) -> str:
         caption = unescape(
             text.replace("\n", " ").replace("  ", " "),
         )
-        if len(caption) == 0:
+        if len(caption) == 0 or is_spaces_only(caption):
             continue
         try:
             duration = float(child.attrib["dur"])