Fix issues with DEL on Mac on empty regex exprn
Fix issues with DEL on Mac on empty regex exprn

On Mac and error is thrown if the regex expression to regcomp() is empty.

Please refer to comments at:
https://github.com/jarun/nnn/commit/c42df81ae5f1206ee586d4e2f236c77f1f0dfbbe

jarun/nnn,jarun/noice,jarun/nnn,jarun/noice,jarun/nnn,jarun/nnn