create_changelog.pl: Collect malformed lines under UNSPECIFIED group.

Fix warnings:
Use of uninitialized value $2 in substitution (s///) at ../qtsdk/packaging-tools/create_changelog.pl line 82, <FOREACH> line 255.
Use of uninitialized value $entry{"text"} in substitution (s///) at ../qtsdk/packaging-tools/create_changelog.pl line 83, <FOREACH> line 255.

Change-Id: Iefc36d36b340ff2016a9880c2e1fe08f850e7a12
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>