tests/test-break.c: Only test Thai breaks with libthai available

The four.break test data file involves the Thai language, meaning that
this test will fail unless we have libthai.  Skip this test unless
libthai is found.

tests/test-break.c

@@ -305,6 +305,12 @@ main (int argc, char *argv[])
       if (!strstr (name, "break"))
         continue;
 
+#ifndef HAVE_LIBTHAI
+      /* four.break involves Thai, so only test it when we have libthai */
+      if (strstr (name, "four.break"))
+        continue;
+#endif
+
       path = g_strdup_printf ("/break/%s", name);
       g_test_add_data_func_full (path, g_test_build_filename (G_TEST_DIST, "breaks", name, NULL),
                                  test_break, g_free);