[zeditor] Can't give focus to Combo Flag search box

Steps to recreate:

1. File->New
2. Click the 'Combo Flags' icon in bottom-left Screen Panel; the 'Select Combo Flag' window appears
3. Click the dark blue label search box immediately above the OK, Help, and Cancel buttons
4. Try to type the name of a combo flag; see how nothing happens
5. Click the combo flag list box with the scrollbar
6. Now you can type the name of a combo flag

The search boxes on:

• The 'Select Enemy' window (accesible via Quest->Enemies)
• The 'Select Item' window (accesible via Quest->Items)
• The Equipment tab of the 'Init Data' window (accessible via Quest->Init Data->Equipment)

are also affected.

The "View Script Slots" window when the Alphabetize checkbox is checked (accessible via ZScript->Compile ZScript...->Slots) does gain focus when clicking it, but the visual feedback that this is the case is a dotted line around the listbox above instead of the search box.