chan_pjsip: disallow PJSIP_SEND_SESSION_REFRESH pre-answer execution

This patch makes it so if the PJSIP_SEND_SESSION_REFRESH dialplan function
is called on a channel prior to answering a warning is issued and the
function returns unsuccessful.

ASTERISK-28878 #close

Change-Id: I053f767d10cf3b2b898fa9e3e7c35ff07e23c9bb

channels/pjsip/dialplan_functions.c

@@ -1680,6 +1680,11 @@ int pjsip_acf_session_refresh_write(struct ast_channel *chan, const char *cmd, c
 		return -1;
 	}
 
+	if (ast_channel_state(chan) != AST_STATE_UP) {
+		ast_log(LOG_WARNING, "'%s' not allowed on unanswered channel '%s'.\n", cmd, ast_channel_name(chan));
+		return -1;
+	}
+
 	if (strcmp(ast_channel_tech(chan)->type, "PJSIP")) {
 		ast_log(LOG_WARNING, "Cannot call %s on a non-PJSIP channel\n", cmd);
 		return -1;

doc/CHANGES-staging/pjsip_send_session_refresh.txt

+Subject: chan_pjsip
+
+The PJSIP_SEND_SESSION_REFRESH dialplan function now issues a warning, and
+returns unsuccessful if it's used on a channel prior to answering.