message: fix match_obj use in redex.py
  Summary: Fix earlier bad commit that used match_obj before it was set
diff: @@ -312,8 +312,8 @@ 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)
  + if match_obj:
  unmangled = match_obj.group(1)
  mangled = match_obj.group(2)
  redex_dict[unmangled] = mangled
  