vim-patch:8.1.2172: spell highlight is wrong at start of the line

Problem:    Spell highlight is wrong at start of the line.
Solution:   Fix setting the "v" variable. (closes vim/vim#5078)
vim/vim@7751d1d

Author: janlazo

src/nvim/screen.c

@@ -3476,6 +3476,7 @@ win_line (
          * Only do this when there is no syntax highlighting, the
          * @Spell cluster is not used or the current syntax item
          * contains the @Spell cluster. */
+        v = (long)(ptr - line);
         if (has_spell && v >= word_end && v > cur_checked_col) {
           spell_attr = 0;
           if (!attr_pri) {

src/nvim/testdir/check.vim

@@ -0,0 +1,11 @@
+source shared.vim
+source term_util.vim
+
+" Command to check that making screendumps is supported.
+" Caller must source screendump.vim
+command CheckScreendump call CheckScreendump()
+func CheckScreendump()
+  if !CanRunVimInTerminal()
+    throw 'Skipped: cannot make screendumps'
+  endif
+endfunc

src/nvim/testdir/test_spell.vim

@@ -1,10 +1,13 @@
 " Test spell checking
 " Note: this file uses latin1 encoding, but is used with utf-8 encoding.
 
+source check.vim
 if !has('spell')
   finish
 endif
 
+source screendump.vim
+
 func TearDown()
   set nospell
   call delete('Xtest.aff')
@@ -477,6 +480,44 @@ func RunGoodBad(good, bad, expected_words, expected_bad_words)
   bwipe!
 endfunc
 
+func Test_spell_screendump()
+  CheckScreendump
+
+  let lines =<< trim END
+       call setline(1, [
+             \ "This is some text without any spell errors.  Everything",
+             \ "should just be black, nothing wrong here.",
+             \ "",
+             \ "This line has a sepll error. and missing caps.",
+             \ "And and this is the the duplication.",
+             \ "with missing caps here.",
+             \ ])
+       set spell spelllang=en_nz
+  END
+  call writefile(lines, 'XtestSpell')
+  let buf = RunVimInTerminal('-S XtestSpell', {'rows': 8})
+  call VerifyScreenDump(buf, 'Test_spell_1', {})
+
+  let lines =<< trim END
+       call setline(1, [
+             \ "This is some text without any spell errors.  Everything",
+             \ "should just be black, nothing wrong here.",
+             \ "",
+             \ "This line has a sepll error. and missing caps.",
+             \ "And and this is the the duplication.",
+             \ "with missing caps here.",
+             \ ])
+       set spell spelllang=en_nz
+  END
+  call writefile(lines, 'XtestSpell')
+  let buf = RunVimInTerminal('-S XtestSpell', {'rows': 8})
+  call VerifyScreenDump(buf, 'Test_spell_1', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('XtestSpell')
+endfunc
+
 let g:test_data_aff1 = [
       \"SET ISO8859-1",
       \"TRY esianrtolcdugmphbyfvkwjkqxz-\xEB\xE9\xE8\xEA\xEF\xEE\xE4\xE0\xE2\xF6\xFC\xFB'ESIANRTOLCDUGMPHBYFVKWJKQXZ",