Returns a new instance with URL patterns from the current instance ("this") and
the "other" instance as follows:
If there are patterns in both instances, combine the patterns in "this" with
the patterns in "other" using PathMatcher.combine(String, String).
Compare the two conditions based on the destination patterns they contain.
Patterns are compared one at a time, from top to bottom via
If all compared patterns match equally, but one instance has more patterns,
it is considered a closer match.
It is assumed that both instances have been obtained via
getMatchingCondition(Message) to ensure they contain only patterns
that match the request and are sorted with the best matches on top.