Regression 16.8.1: "Multiline" Find breakage

Multiline Find is now “behaving badly” as of around 16.8.1 (although it could be from earlier).

Since the symptoms are hard to explain, I’m putting them with steps to reproduce:

1. Open a New document.
2. Hit Ctrl+F to bring up the find dialog
3. If “Multiline” is not enabled, things appear okay.
3.1. Notice that if there’s any text in the Find field, it’s automatically focused and selected
4. Click the “>” button to the right of the Find field and select “Multiline”.
4.1. Notice that the Find field is now multiple lines.
4.2. Click the “>” button again and notice that “Multiline” is checked
5. Now close the find dialog with the ESC key or the Close button
6. Hit Ctrl+F again to bring up the find dialog
7. Problems follow:
7.1. Notice that the Find field is rendered as a single line
7.2. Notice that text in the Find field is not selected as it should be when the Find dialog is opened
7.3. Click the “>” button and notice that “Multiline” is not checked
7.4. Resize the Find dialog and notice that the Find field suddenly becomes multiline