Fix use freed pointer in return value from call thread

(issue ASTERISK-19663)
Reported by: Matt Jordan
Patches:
  ASTERISK-19663-ooh323.patch (License #5415)
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Merged revisions 364649 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 364651 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@364652 65c4cc65-6c06-0410-ace0-fbb531ad65f3

addons/ooh323cDriver.c

@@ -124,7 +124,7 @@ void* ooh323c_call_thread(void* dummy)
  free(mycthread);
  ast_module_unref(myself);
  ast_update_use_count();
- return dummy;
+ return NULL;
 }
 
 int ooh323c_start_call_thread(ooCallData *call) {