Quick evaluation fails when input contains characters from supplementary planes

[edoardopirovano]

Describe the bug
When selecting QL containing a UTF-32 character from the supplementary planes (i.e. not in UTF-16), Quick Eval always deems this to be an invalid target for quick evaluation.

To Reproduce
Include a QL string "😊" somewhere in a QL file. Select it and try to quick evaluate it.

Expected behavior
Quick evaluation is performed with the string 😊 as a result. Note the output of the engine is not particularly well defined for strings containing characters from the supplementary plane, but we should at least pass the quick eval along for the engine to decide what to do with it.