Avoid consolidating invalid ranges

When an invalid range appears the following error arise:

Can't call method "consolidate" on an undefined value at /usr/share/perl5/Dpkg/Copyright/Scanner.pm line 731.

This issue can been seen in packages like texlive-extra.

In order to fix the issue only consolidate valid ranges.

Signed-off-by: Walter Lozano walter.lozano@collabora.com