sanity-check hashindex HashHeader values before using them

[ThomasWaldmann]

If borg reads a hashindex from disk (e.g. the repository index), it should better do some sanity checks on the header values before using them:

• hashindex-fixes-1.4 hashindex: check values in read HashHeader, fixes #9485 #9507
• hashindex-fixes-1.2 hashindex: check values in read HashHeader, fixes #9485 #9508
• hashindex-fixes-1.1 hashindex: check values in read HashHeader, fixes #9485 #9509

Thanks to @rolandrc for finding and reporting this.

[ThomasWaldmann]

@bket @FelixSchwarz @LocutusOfBorg (and other dist package maintainers):

The 1.4 fix will be in upcoming 1.4.4 release or you could cherry-pick the patch from 1.4-maint branch.

1.2.x and 1.1.x in the respective maintenance branches to cherry-pick from there, no new 1.2.x or 1.1.x releases anymore from me.

[ThomasWaldmann]

Fixed, does not affect master branch.