Fix some code that was supposed to ensure that a buffer was terminated, but was

writing to the wrong byte.  Also, remove some non-thread safe test code.

(closes issue #11317)
Reported by: IgorG
Patches:
      unistim-2.patch uploaded by IgorG (license 20)
	  - additional changes by me


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@89484 65c4cc65-6c06-0410-ace0-fbb531ad65f3