patch 8.1.2268: spell file flag zero is not recognized

Problem:    Spell file flag zero is not recognized.
Solution:   Use -1 as an error value, so that zero can be used as a valid flag
            number.
diff --git a/src/testdir/test_spell.vim b/src/testdir/test_spell.vim
index 146e421..c3b2d44 100644
--- a/src/testdir/test_spell.vim
+++ b/src/testdir/test_spell.vim
@@ -290,9 +290,9 @@
         \ ])
 
   call LoadAffAndDic(g:test_data_aff7, g:test_data_dic7)
-  call RunGoodBad("meea1 meea\xE9 bar prebar barmeat prebarmeat  leadprebar lead tail leadtail  leadmiddletail",
+  call RunGoodBad("meea1 meezero meea\xE9 bar prebar barmeat prebarmeat  leadprebar lead tail leadtail  leadmiddletail",
         \ "bad: mee meea2 prabar probarmaat middle leadmiddle middletail taillead leadprobar",
-        \ ["bar", "barmeat", "lead", "meea1", "meea\xE9", "prebar", "prebarmeat", "tail"],
+        \ ["bar", "barmeat", "lead", "meea1", "meea\xE9", "meezero", "prebar", "prebarmeat", "tail"],
         \ [
         \   ["bad", ["bar", "lead", "tail"]],
         \   ["mee", ["meea1", "meea\xE9", "bar"]],
@@ -746,6 +746,9 @@
       \"SFX 61003 Y 1",
       \"SFX 61003 0 meat .",
       \"",
+      \"SFX 0 Y 1",
+      \"SFX 0 0 zero .",
+      \"",
       \"SFX 391 Y 1",
       \"SFX 391 0 a1 .",
       \"",
@@ -757,7 +760,7 @@
       \ ]
 let g:test_data_dic7 = [
       \"1234",
-      \"mee/391,111,9999",
+      \"mee/0,391,111,9999",
       \"bar/17,61003,123",
       \"lead/2",
       \"tail/123",