message: don't die on field/method rename lines
  Summary: Redex unstable will soon generate a proguard rename map that redex stable redex.py can't parse. So, future-proof redex.py on both sides for now.
diff: @@ -312,6 +312,7 @@ def update_proguard_mapping_file(pg_map, redex_map, output_file):
  cls_regex = re.compile(r'^(.*) -> (.*):')
  redex_dict = {}
  for line in redex_map:
  + if match_obj:
  match_obj = cls_regex.match(line)
  unmangled = match_obj.group(1)
  mangled = match_obj.group(2)
  