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




git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@364635 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/logger.c

@@ -1383,6 +1383,9 @@ 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, '/'))) {