Resolves: bug 297221
    Bug Description: rhds71 Malformed Dynamic Authorization Group makes Directory Server Crash
    Reviewed by: nhosoi (Thanks!)
    Fix Description: The problem was that we were not checking the return value of slapi_str2filter().  I added a check at the crash site, and it will not print out a helpful error message.  I did a search through the code looking for other similar places and found a couple.  I added similar code in those places.
    I added an initialization of a buffer to null, as suggested by nhosoi.
    Platforms tested: RHEL5 x86_64
    Flag Day: no
    Doc impact: no