lib/deltas: Squash Coverity warning for div-by-zero in delta show

lib/deltas: Squash Coverity warning for div-by-zero in delta show

If a delta happens to have zero objects, we could end up doing
a divide-by-zero when inferring endianness.  In practice,
a zero-object delta isn't possible to generate I think, but
let's make sure the code is defensive all the same.

Spotted by Coverity.

Coverity CID: 1452208

Closes: #1041
Approved by: pwithnall