patch 8.0.0991: using wrong character conversion for DBCS

Problem:    Using wrong character conversion for DBCS.
Solution:   Use utf_char2bytes instead of mb_char2bytes. (Yasuhiro Matsumoto,
            closes #2012)
diff --git a/src/terminal.c b/src/terminal.c
index 7fadbb6..67c065c 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -945,7 +945,7 @@
 			width = 1;
 			vim_memset(p + pos.col, 0, sizeof(cellattr_T));
 			if (ga_grow(&ga, 1) == OK)
-			    ga.ga_len += mb_char2bytes(' ',
+			    ga.ga_len += utf_char2bytes(' ',
 					     (char_u *)ga.ga_data + ga.ga_len);
 		    }
 		    else
@@ -1943,7 +1943,7 @@
 		    break;
 		}
 		for (i = 0; (c = cells[col].chars[i]) > 0 || i == 0; ++i)
-		    ga.ga_len += mb_char2bytes(c == NUL ? ' ' : c,
+		    ga.ga_len += utf_char2bytes(c == NUL ? ' ' : c,
 					     (char_u *)ga.ga_data + ga.ga_len);
 		p[col].width = cells[col].width;
 		p[col].attrs = cells[col].attrs;
diff --git a/src/version.c b/src/version.c
index 9dc93f2..a0ce86d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    991,
+/**/
     990,
 /**/
     989,