The timezone byte is a signed value, treat it as such.

Otherwise, time zone information for time zones west of
GMT gets discarded.

PR:		kern/128934
Submitted by:	J.R. Oldroyd
MFC after:	4 days

sys/fs/cd9660/cd9660_node.c

@@ -241,7 +241,7 @@ cd9660_tstamp_conv7(pi,pu,ftype)
 	minute = pi[4];
 	second = pi[5];
 	if(ftype != ISO_FTYPE_HIGH_SIERRA)
-		tz = pi[6];
+		tz = ((signed char *)pi)[6]; /* Timezone value is signed. */
 	else
 		/* original high sierra misses timezone data */
 		tz = 0;