Obscure bug in FileCore

I spotted this serendipitously when mistakenly trying to create a directory on a drive that was reporting “Bad free space in Map”.

An Abort is triggered in FindErrBlock line 943 with R0=FFFFFFFE. R14 indicates it was called by OsFunEntry line 144 and that in turn was jumped too from line 70 when OSFunEntry was called with a bad Function number (FFFFFFFF it would seem.)

I believe the issue is OSFunBack not setting R0 to a valid FileCore error number or valid error pointer before calling FindErrBlock.

I’m not entirely sure how OSFunEntry was called with R0=-1 in the first place, so there’s possibly a further underlying issue.