check if active state before stopping pdcp entity

lib/src/upper/pdcp.cc

@@ -53,9 +53,11 @@ void pdcp::init(srsue::rlc_interface_pdcp *rlc_, srsue::rrc_interface_pdcp *rrc_
 void pdcp::stop()
 {
   for(uint32_t i=0;i<SRSLTE_N_RADIO_BEARERS;i++) {
+    if (pdcp_array[i].is_active()) {
       pdcp_array[i].stop();
     }
   }
+}
 
 void pdcp::reestablish() {
   for(uint32_t i=0;i<SRSLTE_N_RADIO_BEARERS;i++) {