Big primary image prevents FOTA

Hey there,

while developing a rather huge application (~97% FLASH used) for the nRF9160, we encountered the problem, that when triggering a FOTA via lwm2m, it fails.

The updatefile is downloaded correctly, but it's the update process which fails when executing after reboot with a  W: Not enough free space to run swap upgrade error.

The issue seems to be, that there is no completely free sector to swap (We are using the default CONFIG_BOOT_SWAP_USING_MOVE.updatescheme). So far this is the expected behaviour, but is it possible to recognise this state at compile time and throw an warning or even abort compiling when having FOTA activated?

This issue can be quite harmful to devices used in the field.

Thanks for your help :)

ncs v.1.5.1
zephyr v.2.4.99