Fix a few more crashes.
One has to do with the string decoder.  In that case, just return an empty string and print the offending characters to the log.  The other has to do with a backlog request event being null.  In that case, just ignore the request.  The last was discovered by running IRCfuzz.c and was fixed by not throwing exceptions from CoreConnService.
Merge pull request #138 from mamarley/morecrashfixes

Fix a few more crashes.