[BUGFIX] Respect excluded parameters on chash revalidation

When decoding the current URL, there might be GET vars that need
to be excluded from cHash calculation due to settings in the
t3lib_cacheHash object.
Reincerting a potentially cached cHash should only be done of
the remaining GET vars are meant to influence the cHash.

Change-Id: I310a9568f6ab679cdf6bbbd9990712936723ecfd
Resolves: #51287