Fix a decoding bug in Solo block-structure descriptions.

Due to a copy-and-paste error, I was accidentally treating 'y' as the
special-case character which puts no 1 bit after the run of 0s, which
should have been 'z'. Game id 9jk#12345-5994 failed an assertion as a
result (because it generates a y which was accidentally treated as
special).

solo.c

@@ -3840,7 +3840,7 @@ static char *spec_to_dsf(const char **pdesc, int **pdsf, int cr, int area)
 	}
 	desc++;
 
-	adv = (c != 25);	       /* 'z' is a special case */
+	adv = (c != 26);	       /* 'z' is a special case */
 
 	while (c-- > 0) {
 	    int p0, p1;