patch 8.2.0945: cannot use "z=" when 'spell' is off

Problem:    Cannot use "z=" when 'spell' is off.
Solution:   Make "z=" work even when 'spell' is off. (Christian Brabandt,
            Gary Johnson, closes #6227)
diff --git a/src/globals.h b/src/globals.h
index 66b204b..27a8d68 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -1581,6 +1581,9 @@
 #if defined(UNIX) || defined(FEAT_SYN_HL) || defined(FEAT_SPELL)
 EXTERN char e_isadir2[]		INIT(= N_("E17: \"%s\" is a directory"));
 #endif
+#ifdef FEAT_SPELL
+EXTERN char e_no_spell[]	INIT(= N_("E756: Spell checking is not possible"));
+#endif
 #ifdef FEAT_LIBCALL
 EXTERN char e_libcall[]	INIT(= N_("E364: Library call failed for \"%s()\""));
 #endif