improve status indication of Flash Firmware panel

[pitts-mo]

File selection status "No file chosen" is erroneously reported during and after the first flash attempt.

The images below are from a bootloader flash before flashing, after selecting a bootloader file, during flash of bootloader and finally the first image represents the display after flashing a bootloader.

Note: Additional flash attempts do appear to flash the previously selected bootloader (no need to re-select).

eg: