Prevent a potential crash when using manager hooks.

Found by me while poking at DPMA-127.
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Merged revisions 364841 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 364842 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@364844 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/manager.c

@@ -4226,7 +4226,7 @@ static int action_originate(struct mansession *s, const struct message *m)
 		ast_parse_allow_disallow(NULL, cap, codecs, 1);
 	}
 
-	if (!ast_strlen_zero(app)) {
+	if (!ast_strlen_zero(app) && s->session) {
 		int bad_appdata = 0;
 		/* To run the System application (or anything else that goes to
 		 * shell), you must have the additional System privilege */