Add code check to avoid access violation.

Signed-off-by: ydong10
Reviewed-by: rsun3

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13014 6f19259b-4bc3-4df7-8a09-765794883524

MdeModulePkg/Universal/Network/IScsiDxe/IScsiProto.c

@@ -403,6 +403,7 @@ IScsiReceiveLoginRsp (
   //
   // A Login Response is received, process it.
   //
+  ASSERT (Pdu != NULL);
   Status = IScsiProcessLoginRsp (Conn, Pdu);
 
   NetbufFree (Pdu);