Enable LV overlays on "Card full/write protected" (and supress them if possible)

[gotar]

Having non writable card (either full or r/o) issues fullscreen warning and makes LV unusable. One might think it doesn't matter as shutter button doesn't work either, but when tethering it is reenabled and I can take remote shots (at least with my 500D) directly into my Linux box. However, with no advanced ML functions - the basic draws including histogram, waveform and vectoroscope are available by some trick: enter into ML menu (trash button) and make it transparent (zoom in button). This would be more convinient to get rid of the original Canon's warning (just highlight it in place, where available photo count usually resides) and try to fully operate, with no artificial restrains (at least when PC is connected, but some LV image analysis even without r/w possibility might be a support for taking pictures with another, less-featured camera).

Of course one might say 'put writable card', but in case of tethering it does nothing except wearing the card, power usage and some slowdown, as pictures are eventually removed from the card anyway. The card is needed only for running ML and might be small and slow.