We're seeing parse errors on constraints with no markers, possibly
related to a unicode issue (it only seems to happen when the empty
marker string is a unicode string). There isn't any point in doing an
expensive comparison when there are no markers for the constraint, so
skip them in that part of the search loop.
Change-Id: I2a700fb8f3e776faf6123c9924d87add12324ef2
Signed-off-by: Doug Hellmann <doug@doughellmann.com>