Call OnDelChan prior to unsetting extensibles

cs_set uses this to set -P on permanent channels if they are persistent.

Also move similar event in nickcore/nickalias destruction

src/nickalias.cpp

@@ -50,10 +50,10 @@ NickAlias::NickAlias(const Anope::string &nickname, NickCore* nickcore) : Serial
 
 NickAlias::~NickAlias()
 {
-	UnsetExtensibles();
-
 	FOREACH_MOD(OnDelNick, (this));
 
+	UnsetExtensibles();
+
 	/* Accept nicks that have no core, because of database load functions */
 	if (this->nc)
 	{