Fix Pattern row clues when a row has no black in

I'd failed to initialise the row clue string to empty so it got the
contents of the previous row to be displayed.  This could only happen
for imported descriptions, or for puzzles with one or two columns.

Thanks to Glen Sawyer for spotting and reporting the bug.

1 files changed, 1 insertions, 0 deletions

diff --git a/pattern.c b/pattern.c
index 92d8a79..489eb54 100644
--- a/pattern.c
+++ b/pattern.c
@@ -1841,6 +1841,7 @@ static void draw_numbers(
         size_t off = 0;
 
         assert(rowlen <= state->common->rowsize);
+        *ds->strbuf = '\0';
         for (j = 0; j < rowlen; j++)
             off += sprintf(ds->strbuf + off, "%s%d", j ? "  " : "", rowdata[j]);
         y = ry;