[fpc-pascal] Last fix for RegExpr (error on empty input)

[AlexeyT]

1) typo in new Id: iMput.

2) wrong fix for 2nd "Error" call in Substitute(): you disabled Error 
call but didn't disable Exit, you need to skip Exit there too, so 
Substitute will return non empty result when user replaces regex "\b" to 
e.g. "__".

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Regards,
Alexey