Fix problems with controls when naming files

When I click Export As, it brings up a box where I can set the file name and location. But using the arrow keys does not move the cursor within the filename. It moves the active frame in the viewer (left/right arrows) or active clip (up/down arrows) just like it does normally.

This is confusing and counterproductive. While the export box is present, the arrow keys should move within the filename text like they do in any other program.