11416 smbios_info_slot_peers() gets NULL check wrong

@@ -19,11 +19,11 @@
  * CDDL HEADER END
  */
 
 /*
  * Copyright 2015 OmniTI Computer Consulting, Inc.  All rights reserved.
- * Copyright (c) 2018, Joyent, Inc.
+ * Copyright 2019 Joyent, Inc.
  * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
 
 /*

@@ -696,18 +696,20 @@
 int
 smbios_info_slot_peers(smbios_hdl_t *shp, id_t id, uint_t *npeers,
     smbios_slot_peer_t **peerp)
 {
         const smb_struct_t *stp = smb_lookup_id(shp, id);
-        const smb_slot_t *slotp = (const smb_slot_t *)stp->smbst_hdr;
+        const smb_slot_t *slotp;
         smbios_slot_peer_t *peer;
         size_t minlen;
         uint_t i;
 
         if (stp == NULL)
                 return (-1); /* errno is set for us */
 
+        slotp = (const smb_slot_t *)stp->smbst_hdr;
+
         if (stp->smbst_hdr->smbh_type != SMB_TYPE_SLOT)
                 return (smb_set_errno(shp, ESMB_TYPE));
 
         if (stp->smbst_hdr->smbh_len <= offsetof(smb_slot_t, smbsl_npeers) ||
             slotp->smbsl_npeers == 0) {