Can disallow isset & unset

[spaze]

What's new

• Can disallow isset() in disallowedFunctionCalls (feat: support isset() language construct #289, thanks @ksaveras!)
• Can disallow unset, too (You can now disallow unset, too #291)

Internal change

• array_merge arrays with error messages only when not empty, this should speed things up a bit, maybe (array_merge arrays only when not empty, this should speed things up a bit #287)

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This discussion was created from the release Can disallow `isset` & `unset`.