Black Magic App received signal SIGFPE, Arithmetic exception.

[HZFrodo]

#1323 introduce a bug, it will division by zero when f->writesize is zero
I observe this bug when trying to debug LPC MCU

[dragonmux]

Thanks for the report HZFrodo - this is actually already fixed in #1415 which is pending review and merge. Please give the PR branch a try and let us know how you get on.