utils.parseModes: be a bit more fault-tolerant

- Log "mode requires an argument but none was found" errors to warning, and skip the mode instead of failing completely.
- Assign a fallback value for 'prefix', checking to make sure it exists and raising ValueError (not UnboundLocalError) when it doesn't.

utils.py

@@ -94,6 +94,7 @@ def parseModes(irc, target, args):
     # C = Mode that changes a setting and only has a parameter when set.
     # D = Mode that changes a setting and never has a parameter.
     usermodes = not isChannel(target)
+    prefix = ''
     modestring = args[0]
     if not modestring:
         return ValueError('No modes supplied in parseModes query: %r' % modes)
@@ -109,8 +110,11 @@ def parseModes(irc, target, args):
         if mode in '+-':
             prefix = mode
         else:
+            if not prefix:
+                raise ValueError('Invalid query %r: mode char given without preceding prefix.' % modestring)
             arg = None
             log.debug('Current mode: %s%s; args left: %s', prefix, mode, args)
+            try:
                 if mode in (supported_modes['*A'] + supported_modes['*B']):
                     # Must have parameter.
                     log.debug('Mode %s: This mode must have parameter.', mode)
@@ -123,6 +127,11 @@ def parseModes(irc, target, args):
                     # Only has parameter when setting.
                     log.debug('Mode %s: Only has parameter when setting.', mode)
                     arg = args.pop(0)
+            except IndexError:
+                log.warning('(%s/%s) Error while parsing mode %r: mode requires an '
+                            'argument but none was found. (modestring: %r)',
+                            irc.name, target, mode, modestring)
+                continue  # Skip this mode; don't error out completely.
             res.append((prefix + mode, arg))
     return res