Dial API: Prevent crash on NULL cap

This prevents a crash in the Dial API triggered by use of the Page()
application where a format capability struct was used before checking
whether it was NULL.

ASTERISK-24074 #close


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@419111 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/dial.c

@@ -300,7 +300,7 @@ static int begin_dial_prerun(struct ast_dial_channel *channel, struct ast_channe
 	/* Copy device string over */
 	ast_copy_string(numsubst, channel->device, sizeof(numsubst));
 
-	if (ast_format_cap_count(cap)) {
+	if (cap && ast_format_cap_count(cap)) {
 		cap_request = cap;
 	} else if (chan) {
 		cap_request = ast_channel_nativeformats(chan);