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/nickcore.cpp

@@ -37,10 +37,10 @@ NickCore::NickCore(const Anope::string &coredisplay) : Serializable("NickCore"),
 
 NickCore::~NickCore()
 {
-	UnsetExtensibles();
-
 	FOREACH_MOD(OnDelCore, (this));
 
+	UnsetExtensibles();
+
 	if (!this->chanaccess->empty())
 		Log(LOG_DEBUG) << "Non-empty chanaccess list in destructor!";