dep-resolv: Fix bug handling negated dependencies.
Fix bug spotted by @ouwerkerk in handling of negated dependencies. Since
_shortenModuleNames() removes all text from beginning of the string to
the first '/', and since module names in dependency-data almost always
contain at least one '/', the '-' prefix that indicates a negated
dependency is eaten before the dependency is inserted into the
This seems to have not been a significant issue in practice but could
help with building fewer modules for things like Android-related
branch-groups (which ignores kf5umbrella and manually specifies a
minimal dependency list instead).