Fix: Undefined tab panel TypeError in CreateWiki form

[sentry]

This commit addresses a TypeError: undefined is not an object (evaluating 'panel.$element') that occurs in modules/ext.createwiki.oouiform.ooui.js.

The root cause was identified as enhancePanel() being called with an undefined panel object. This happened because switchCreateWikiTab() was invoked with an undefined tab name (derived from $("[id*=mw-section-]").attr("id") when no such element existed on pages like Special:RequestWikiQueue), causing tabs.getCurrentTabPanel() to return undefined.

The fix implements two safeguards:

1. A null guard has been added at the beginning of the enhancePanel() function to prevent dereferencing $element on an undefined panel.
2. In the hashchange event handler, specifically for the hash === '' branch, a check has been added to ensure that $("[id*=mw-section-]") actually finds an element before attempting to retrieve its id and call switchCreateWikiTab.

Fixes MEDIAWIKI-CC8

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