Drop 1991/fine back to its original 80 chars

With more clever use of the Makefile the number of characters is back
down to 80 which is what the original was!

This also fixes the warning that was introduced when it was dropped back
down to 85. 'B' is defined as '(int)b' which is used in two places where
a cast is necessary or otherwise will silent a warning.

The README.md file has been checked and this should complete this entry
now.

1991/fine/README.md

@@ -33,8 +33,8 @@ This filter, 80 chars plus a newline, fits into a single line on most
 terminals (unless your terminal has a line wrap mis-feature :-)).
 
 Note in 2023: fixing this entry to work with modern systems increased the size,
-originally to 106 characters but dropped down to 85 with clever use of the
-Makefile and removal of a cast that was not strictly necessary.
+originally to 106 characters but it was dropped back down to 80 with clever use
+of the Makefile.
 
 This entry is likely one of the smallest C implementations of this
 filter, excluding programs that resort to command line or include