pbx.c: Pre-initialize timezone to avoid crash on destroy

In ast_build_timing, initialize the timezone value to NULL
in order to avoid deferencing an uninitialized value later
when calling ast_destroy_timing.  The timezone value could
be uninitialized if ast_build_timing were to fail due to a
zero length time string.

(closes issue ASTERISK-22861)
Reported by: Sebastian Murray-Roberts
Review: https://reviewboard.asterisk.org/r/3134/
Patches:
     ast_build_timing-initialize-timezone.patch uploaded by coreyfarrell (license 5909)
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Merged revisions 406241 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 406245 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 406264 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@406269 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/pbx.c

@@ -9167,6 +9167,8 @@ int ast_build_timing(struct ast_timing *i, const char *info_in)
 	char *info;
 	int j, num_fields, last_sep = -1;
 
+	i->timezone = NULL;
+
 	/* Check for empty just in case */
 	if (ast_strlen_zero(info_in)) {
 		return 0;
@@ -9186,8 +9188,6 @@ int ast_build_timing(struct ast_timing *i, const char *info_in)
 	/* save the timezone, if it is specified */
 	if (num_fields == 5) {
 		i->timezone = ast_strdup(info + last_sep + 1);
-	} else {
-		i->timezone = NULL;
 	}
 
 	/* Assume everything except time */

utils/extconf.c

@@ -4453,6 +4453,8 @@ int ast_build_timing(struct ast_timing *i, const char *info_in)
 	char *info;
 	int j, num_fields, last_sep = -1;
 
+	i->timezone = NULL;
+
 	/* Check for empty just in case */
 	if (ast_strlen_zero(info_in)) {
 		return 0;
@@ -4472,8 +4474,6 @@ int ast_build_timing(struct ast_timing *i, const char *info_in)
 	/* save the timezone, if it is specified */
 	if (num_fields == 5) {
 		i->timezone = ast_strdup(info + last_sep + 1);
-	} else {
-		i->timezone = NULL;
 	}
 
 	/* Assume everything except time */