timestamps shouldn't show up when in screenshot mode

Bug report

Thanks for filing an issue! Please answer the questions below so I can help you.

• iTerm2 version: Build 3.5.3
• OS version:
• Attach `` here (drag-drop from finder into this window) com.googlecode.iterm2.plist/com.googlecode.iterm2.plist
• Attach a debug log, if possible.
• Attach a screen capture video if it would make the reproduction steps clearer.

Attaching a screen capture is hard because the problem only occurs when in the screenshot prepare tool 😁

PLEASE ATTACH YOUR PLIST FILE FOR BUG REPORTS! Seriously! I'll probably ask you for it if you don’t.

Detailed steps to reproduce the problem

1. enable "Show timestamps When mouse hovers over scroll bar"
2. Move your mouse to the left-hand side of the terminal window (so it's not near the scroll bar)
3. enter screenshot mode with Command+Shift+4
4. Hover over scroll bar

What happened

Timestamps show up

What should have happened

Timestamps don't show up.

Why I think this is a bug

Most apps preserve the hover state when you begin the screenshot tool. For example, if I hover over a button in Edge and then begin a screenshot, the button I have selected will continue to be in the hover state no matter where I move the screenshot selector.

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