Use size_t in LSET::FmtHex to match size() call and add unit test
OOB memory access caught by the MSVC debugger. Triggered by the pcbnew autosave for me. LSET was a size of 51 (1 less than a full nibble). The iteration failed to skip the extra non-existent bits when forming the last nibble.
This should also be cherry picked to the 5.1.x branch
Edited by Mark Roszko