Pattern: missing special case in the solver.

Pattern: missing special case in the solver.

We were filling in a row immediately as all-white if it had no clues
at all, but weren't filling in a row as all-black if it had a single
clue covering the entire row. Now we do both.

In particular, this caused the Pattern solver to be unable to take
advantage of one of the two kinds of totally obvious clue across the
_easy_ dimension of a trivial 1xN puzzle - and a special case of
_that_, as a user pointed out, is that the game generator hangs trying
to create a 1x1 puzzle, which ought to be the easiest thing in the
world!