#1547 IncrementalSearch: macOS fix

[Federico Perini]

On macOS, incremental search does not work because every time a key is hit, the search text is reset. so there is always at most 1 character in the search bar.

This fix prevents the text reset during incremental updates (safeguarded for macOS only).

Thank you,
Federico

[Miguel Gimenez]

Applied in [r13713], thank you.

Patch modified to keep code style and remove non-ASCII characters in comment.