Catch two instances of untested regexp matches

They could possibly lead to the problems mentioned in
  https://github.com/OfflineIMAP/offlineimap/issues/6
though there are no sound evidences for this.

Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>

offlineimap/folder/Maildir.py

@@ -104,6 +104,8 @@ class MaildirFolder(BaseFolder):
         oldest_time_utc -= oldest_time_today_seconds
 
         timestampmatch = re_timestampmatch.search(messagename)
+        if not timestampmatch:
+            return True
         timestampstr = timestampmatch.group()
         timestamplong = long(timestampstr)
         if(timestamplong < oldest_time_utc):

offlineimap/imaputil.py

@@ -145,6 +145,10 @@ def imapsplit(imapstring):
         elif workstr[0] == '"':
             # quoted fragments '"...\"..."'
             m = quotere.match(workstr)
+            if not m:
+                raise ValueError ("failed to parse "
+                  "quoted component %s " % str(workstr) + \
+                  "while working with %s" % str(imapstring))
             retval.append(m.group('quote'))
             workstr = m.group('rest')
         else: