Fix bug in hb_language_from_string()

Reported by Jonathan Kew.

src/hb-language.c

diff --git a/src/hb-language.c b/src/hb-language.c
index ff25d7b..5d7286b 100644
--- a/src/hb-language.c
+++ b/src/hb-language.c
@@ -102,6 +102,8 @@
   for (p = (unsigned char *) langs[i]; *p; p++)
     *p = canon_map[*p];
 
+  num_langs++;
+
   return (hb_language_t) langs[i];
 }