engine: decrease instanced baseline index by minus one to avoid zero offset which interpreted as no baseline at all

engine/common/net_encode.c

@@ -1870,7 +1870,7 @@ qboolean MSG_ReadDeltaEntity( sizebuf_t *msg, entity_state_t *from, entity_state
 			}
 			else
 			{
-				baseline_offset = abs( baseline_offset );
+				baseline_offset = abs( baseline_offset + 1 );
 				if( baseline_offset < cl.instanced_baseline_count )
 					from = &cl.instanced_baseline[baseline_offset];
 			}

engine/server/sv_frame.c

@@ -356,7 +356,7 @@ static void SV_EmitPacketEntities( sv_client_t *cl, client_frame_t *to, sizebuf_
 					if( !Q_strcmp( classname, sv.instanced[i].classname ))
 					{
 						baseline = &sv.instanced[i].baseline;
-						offset = -i;
+						offset = -i - 1; // to avoid zero offset
 						break;
 					}
 				}