[2.0.21] The "invalid save filename" error message doesn't restore keyboard focus

[bustafreak]

Repro:

• Attempt to save a filename using a disallowed character, such as "yay!"

Expected: The "invalid character" error message can be dismissed with the Enter or Space keys, and keyboard focus is then returned to the "name your save" text input.

Actual: The "invalid character" error message doesn't have keyboard focus; you must move your hands to the mouse to dismiss it, and then you must again manually click inside the "name your save" text input to restore keyboard focus there and fix your invalid filename.