Fix Coverity Scan CID 340237 (Using variable UE_id as an index to array UE_list->UE_sched_ctrl.)

openair2/LAYER2/MAC/pre_processor.c

@@ -304,6 +304,8 @@ maxround_ul(module_id_t Mod_id, uint16_t rnti, int sched_frame,
   for (CC_id = 0; CC_id < RC.nb_mac_CC[Mod_id]; CC_id++) {
     cc = &RC.mac[Mod_id]->common_channels[CC_id];
     UE_id = find_UE_id(Mod_id, rnti);
+    if(UE_id == -1)
+      continue;
     harq_pid = subframe2harqpid(cc, sched_frame, sched_subframe);
     round = UE_list->UE_sched_ctrl[UE_id].round_UL[CC_id][harq_pid];