compilation failed with -Werror=maybe-uninitialized

The compilation failed for devmode
--enable DONT_OPTIMIZE
--enable BETTER_BACKTRACES
--enable DO_CRASH
--enable TEST_FRAMEWORK

res_pjsip/pjsip_configuration.c: In function dtls_handler:
res_pjsip/pjsip_configuration.c:974:20: error:
back may be used uninitialized in this function [-Werror=maybe-uninitialized]
int size = strlen(front);
           ^
cc1: all warnings being treated as errors

Change-Id: I7f082ead0312792a577ec7c73015ba64dabca580

res/res_pjsip/pjsip_configuration.c

@@ -963,7 +963,9 @@ static int dtls_handler(const struct aco_option *opt,
 {
 	struct ast_sip_endpoint *endpoint = obj;
 	char *name = ast_strdupa(var->name);
-	char *front, *back, *buf = name;
+	char *front = NULL;
+	char *back = NULL;
+	char *buf = name;
 
 	/* strip out underscores in the name */
 	front = strtok_r(buf, "_", &back);