Do not mix raw and cooked lengths for trimming logic

include/sardine.py

         suffix = u'…'
         cooked = raw.decode("utf-8")
         if self.plugindata.fmt == "plain":
-            if self.plugindata.maxlen and len(raw) > self.plugindata.maxlen:
+            if self.plugindata.maxlen and len(cooked) > self.plugindata.maxlen:
                 newlen = self.plugindata.maxlen - len(suffix)
                 cooked = cooked[:newlen] + suffix
         return cooked.encode("utf-8")