patch 9.0.0024: may access part of typeahead buf that isn't filled

Problem:    May access part of typeahead buf that isn't filled.
Solution:   Check length of typeahead.

Author: brammool

src/getchar.c

@@ -2437,7 +2437,8 @@ handle_mapping(
     int		is_plug_map = FALSE;
 
     // If typehead starts with <Plug> then remap, even for a "noremap" mapping.
-    if (typebuf.tb_buf[typebuf.tb_off] == K_SPECIAL
+    if (typebuf.tb_len >= 3
+	    && typebuf.tb_buf[typebuf.tb_off] == K_SPECIAL
 	    && typebuf.tb_buf[typebuf.tb_off + 1] == KS_EXTRA
 	    && typebuf.tb_buf[typebuf.tb_off + 2] == KE_PLUG)
 	is_plug_map = TRUE;

src/version.c

@@ -735,6 +735,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    24,
 /**/
     23,
 /**/