patch 8.2.4233: crash when recording and using Select mode

Problem:    Crash when recording and using Select mode.
Solution:   When deleting the last recorded character check there is something
            to delete.

src/getchar.c

@@ -252,8 +252,11 @@ add_buff(
     static void
 delete_buff_tail(buffheader_T *buf, int slen)
 {
-    int len = (int)STRLEN(buf->bh_curr->b_str);
+    int len;
 
+    if (buf->bh_curr == NULL || buf->bh_curr->b_str == NULL)
+	return;  // nothing to delete
+    len = (int)STRLEN(buf->bh_curr->b_str);
     if (len >= slen)
     {
 	buf->bh_curr->b_str[len - slen] = NUL;

src/testdir/test_registers.vim

@@ -739,6 +739,15 @@ func Test_record_in_insert_mode()
   bwipe!
 endfunc
 
+func Test_record_in_select_mode()
+  new
+  call setline(1, 'text')
+  sil norm q00
+  sil norm q
+  call assert_equal('0ext', getline(1))
+  bwipe!
+endfunc
+
 " Make sure that y_append is correctly reset
 " and the previous register is working as expected
 func Test_register_y_append_reset()

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4233,
 /**/
     4232,
 /**/