Script Editor; Find/ Replace, now defaults 'Search in selection' checkbox

When showing the Find/ Replace box in the Script Editor, e.g., by pressing Ctrl+F, the 'Search in selection' checkbox is now checked if:
1. There is selected text.
2. The selected text spans more than one line.

Also, if there is selected text then showing this box clears the 'Search in selection' checkbox.

Previously, the 'Find What' field defaulted to any selected text. This now only defaults to the selected text if the selected text does not span multiple lines.