patch 8.0.0524: folds messed up

Problem:    Folds are messed up when 'encodin' is "utf-8".
Solution:   Also set the fold character when it's not multi-byte.

src/screen.c

@@ -2700,7 +2700,10 @@ fold_line(
                 ScreenLines[off + col] = 0x80; /* avoid storing zero */
 	    }
 	    else
+	    {
 		ScreenLinesUC[off + col] = 0;
+		ScreenLines[off + col] = fill_fold;
+	    }
 	    col++;
 	}
 	else