vim-patch:8.2.3484: crash when going through spell suggestions

Problem:    Crash when going through spell suggestions.
Solution:   Limit the text length for finding suggestions to the original
            length.  Do not update buffers when exiting. (closes vim/vim#8965)
e275ba4fc9

src/nvim/spell.c

@@ -3663,6 +3663,12 @@ static void suggest_try_change(suginfo_T *su)
   p = su->su_badptr + su->su_badlen;
   (void)spell_casefold(curwin, p, (int)STRLEN(p), fword + n, MAXWLEN - n);
 
+  // Make sure the resulting text is not longer than the original text.
+  n = (int)STRLEN(su->su_badptr);
+  if (n < MAXWLEN) {
+    fword[n] = NUL;
+  }
+
   for (int lpi = 0; lpi < curwin->w_s->b_langp.ga_len; ++lpi) {
     lp = LANGP_ENTRY(curwin->w_s->b_langp, lpi);
 

src/nvim/testdir/test_spell_utf8.vim

@@ -768,6 +768,21 @@ func Test_spellfile_value()
   set spellfile=Xdir/Xtest.utf-8.add,Xtest_other.add
 endfunc
 
+func Test_no_crash_with_weird_text()
+  new
+  let lines =<< trim END
+      r<sfile>
+      €
+
+
+      €
+  END
+  call setline(1, lines)
+  exe "%norm \<C-v>ez=>\<C-v>wzG"
+
+  bwipe!
+endfunc
+
 " Invalid bytes may cause trouble when creating the word list.
 func Test_check_for_valid_word()
   call assert_fails("spellgood! 0\xac", 'E1280:')