vim-patch:8.2.4418: crash when using special multi-byte character

Problem:    Crash when using special multi-byte character.
Solution:   Don't use isalpha() for an arbitrary character.
5921aeb574

Rename vim_isalpha to mb_isalpha.

src/nvim/mbyte.c

@@ -1317,6 +1317,12 @@ bool mb_isupper(int a)
   return mb_tolower(a) != a;
 }
 
+bool mb_isalpha(int a)
+  FUNC_ATTR_WARN_UNUSED_RESULT
+{
+  return mb_islower(a) || mb_isupper(a);
+}
+
 static int utf_strnicmp(const char_u *s1, const char_u *s2, size_t n1, size_t n2)
 {
   int c1, c2, cdiff;

src/nvim/path.c

@@ -642,8 +642,7 @@ static size_t do_path_expand(garray_T *gap, const char_u *path, size_t wildoff,
     } else if (path_end >= path + wildoff
                && (vim_strchr((char_u *)"*?[{~$", *path_end) != NULL
 #ifndef WIN32
-                   || (!p_fic && (flags & EW_ICASE)
-                       && isalpha(utf_ptr2char(path_end)))
+                   || (!p_fic && (flags & EW_ICASE) && mb_isalpha(utf_ptr2char(path_end)))
 #endif
                    )) {
       e = p;

src/nvim/testdir/test_autochdir.vim

@@ -64,4 +64,14 @@ func Test_verbose_pwd()
   call delete('Xautodir', 'rf')
 endfunc
 
+func Test_multibyte()
+  " using an invalid character should not cause a crash
+  set wic
+  " E344 is thrown first, but v8.1.1183 hasn't been ported yet
+  " call assert_fails('tc û<><C3BB><EFBFBD>¦*', 'E344:')
+  call assert_fails('tc û<><C3BB><EFBFBD>¦*', 'E472:')
+  set nowic
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab