patch 8.1.1143: may pass weird strings to file name expansion

Problem:    May pass weird strings to file name expansion.
Solution:   Check for matching characters.  Disallow control characters.
diff --git a/src/spell.c b/src/spell.c
index ae4db12..947bee5 100644
--- a/src/spell.c
+++ b/src/spell.c
@@ -2308,11 +2308,14 @@
     /* Loop over comma separated language names. */
     for (splp = spl_copy; *splp != NUL; )
     {
-	/* Get one language name. */
+	// Get one language name.
 	copy_option_part(&splp, lang, MAXWLEN, ",");
 	region = NULL;
 	len = (int)STRLEN(lang);
 
+	if (!valid_spellang(lang))
+	    continue;
+
 	if (STRCMP(lang, "cjk") == 0)
 	{
 	    wp->w_s->b_cjk = 1;