identifications not returned for some files when new -multi droid setting used for signature file

[richardlehane]

The new roy build -multi setting has introduced an error. For a small proportion of files, no identifications are being returned:

There must be a code path in pronom/identifier.go where a nil slice of identifications is returned with config.multi=droid set.

[richardlehane]

resolved with v1.10.1 release