[ie/youtube] Rework nsig function name extraction (#13403)

Closes #13401

Authored by: Grub4K

test/test_youtube_signature.py

@@ -320,6 +320,14 @@ _NSIG_TESTS = [
         'https://www.youtube.com/s/player/59b252b9/player_ias.vflset/en_US/base.js',
         'D3XWVpYgwhLLKNK4AGX', 'aZrQ1qWJ5yv5h',
     ),
+    (
+        'https://www.youtube.com/s/player/fc2a56a5/player_ias.vflset/en_US/base.js',
+        'qTKWg_Il804jd2kAC', 'OtUAm2W6gyzJjB9u',
+    ),
+    (
+        'https://www.youtube.com/s/player/fc2a56a5/tv-player-ias.vflset/tv-player-ias.js',
+        'qTKWg_Il804jd2kAC', 'OtUAm2W6gyzJjB9u',
+    ),
 ]