gitweb: Fix an issue when cloning existing repository

Skip all the other git clone progress log lines. Fixes
occasional `'total_progress' not defined` error.

Tested in the testing container that cloning exisiting repository
works.

Signed-off-by: Veiko Aasa <veiko17@disroot.org>
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>

plinth/modules/gitweb/privileged.py

@@ -145,6 +145,8 @@ def _clone_status_line_to_percent(line):
             total_progress = 10 + 0.6 * progress
         elif 'Resolving deltas' in text:
             total_progress = 70 + 0.3 * progress
+        else:
+            return None
 
         return str(int(total_progress))