Merged revisions 364635 via svnmerge from

https://origsvn.digium.com/svn/asterisk/branches/1.8

........
  r364635 | markm | 2012-04-30 11:51:12 -0400 (Mon, 30 Apr 2012) | 10 lines
  
  Sanatize result from bfd_find_nearest_line (BETTER_BACKTRACES)
  
  bfd_find_nearest_line can possibly set file to null resulting in a crash when strrchr(file) runs
  
  (closes issue ASTERISK-19815)
  Reported by Mark Murawski
  Tested by Mark Murawski
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Merged revisions 364650 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@364654 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/logger.c

@@ -1519,6 +1519,9 @@ char **ast_bt_get_symbols(void **addresses, size_t num_frames)
 					continue;
 				}
 
+				/* file can possibly be null even with a success result from bfd_find_nearest_line */
+				file = file ? file : "";
+
 				/* Stack trace output */
 				found++;
 				if ((lastslash = strrchr(file, '/'))) {