Fix Repository.resolve() to not throw runtime exceptions
resolve() was throwing undocumented runtime exceptions.
ArrayIndexOutOfBoundsException was thrown when it couldn't find commit's
parents and NumberFormatException when it couldn't parse parents number.
Now it returns null when it can't find appropriate commit's parents
and (already checked) RevisionSyntaxException when it can't parse number.
Signed-off-by: Marek Zawirski <marek.zawirski@gmail.com>
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>