Add format length limit to prevent format-truncation warning

[BsAtHome]

A spurious format truncation warning appears when extra warnings are enabled (using g++ 14.2.1). This might be a false positive, but is easily fixed by limiting the expansion size. All the names have a maximum length of 20 characters so limiting the expansion to that length should be fine.

[andypugh]

I suspect that no-one has ever used emclcd, but whilst it exists, it might as well compile cleany.

[BsAtHome]

I suspect that no-one has ever used emclcd, but whilst it exists, it might as well compile cleany.

It may need a caring hand. Well, a firm hand might be required. The code references "/dev/hda1". That is a long time ago I've seen that device.

[andypugh]

It is retained mainly as an example of a user interface using a different paradigm to Python + GUI framework.
It's actually a userinterface running on a particular 4x20 LCD display with integrated buttons intended to mount in the front panel of your PC tower case (which could have been quite a neat installation for a special-purpose CNC machine)
This might be one: https://www.ebay.co.uk/itm/115938873276