[FIX] Using maxValue<>() explicitely in Fiona.

Coverity had a false positive here since the value is never used, but
it does not hurt to use maxValue<unsigned>() explicitely here, either.
[FIX] Preventing possible div-by-0 in fiona.
Merge pull request #612 from holtgrewe/fix/fiona-uninitialized-value

[FIX] Using maxValue<>() explicitely in Fiona.