patch 9.0.1330: handling new value of an option has a long "else if" chain

Problem:    Handling new value of an option has a long "else if" chain.
Solution:   Use a function pointer. (Yegappan Lakshmanan, closes #12015)
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index 7fd0952..0d83980 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -3142,7 +3142,7 @@
     // If the window options were changed may need to set the spell language.
     // Can only do this after the buffer has been properly setup.
     if (did_get_winopts && curwin->w_p_spell && *curwin->w_s->b_p_spl != NUL)
-	(void)did_set_spelllang(curwin);
+	(void)parse_spelllang(curwin);
 #endif
 
     if (command == NULL)