Prevent the saving of invalid timezone string in to the database on the options pages. If an invalid timezone is submitted it is ignored and the setting remains unchanged.
This prevents a warning or fatal (depending on the PHP version) from being thrown by an invalid timezone setting on the Settings > General page.
Props ankit-k-gupta, costdev, huzaifaalmesbah, mrinal013, nicolefurlan, oglekler.
Fixes#58814.
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git-svn-id: http://core.svn.wordpress.org/trunk@56460 1a063a9b-81f0-0310-95a4-ce76da25c4cd