patch 9.0.0412: compiler warning for unused argument

Problem:    Compiler warning for unused argument.
Solution:   Add UNUSED.

src/charset.c

@@ -943,7 +943,7 @@ vim_isprintc_strict(int c)
 init_chartabsize_arg(
 	chartabsize_T	*cts,
 	win_T		*wp,
-	linenr_T	lnum,
+	linenr_T	lnum UNUSED,
 	colnr_T		col,
 	char_u		*line,
 	char_u		*ptr)

src/version.c

@@ -703,6 +703,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    412,
 /**/
     411,
 /**/