patch 8.1.2091: double free when memory allocation fails

Problem:    Double free when memory allocation fails. (Zu-Ming Jiang)
Solution:   Use VIM_CLEAR() instead of vim_free(). (closes #4991)

Author: brammool

src/getchar.c

@@ -1296,11 +1296,11 @@ free_typebuf(void)
     if (typebuf.tb_buf == typebuf_init)
 	internal_error("Free typebuf 1");
     else
-	vim_free(typebuf.tb_buf);
+	VIM_CLEAR(typebuf.tb_buf);
     if (typebuf.tb_noremap == noremapbuf_init)
 	internal_error("Free typebuf 2");
     else
-	vim_free(typebuf.tb_noremap);
+	VIM_CLEAR(typebuf.tb_noremap);
 }
 
 /*

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2091,
 /**/
     2090,
 /**/