Resolve "TDCP batch implementation"

Closes #15 (closed)

src/utils/satellite.cpp

@@ -79,15 +79,16 @@ Satellites computeSatellites(const Observations&             obs,
     //   std::cout << std::endl;
 
     // compute positions
-    satposs(obs.getObservations().front().time,
-            obs.data(),
-            obs.size(),
-            &nav.getNavigation(),
-            eph_opt,
-            rs,
-            dts,
-            var,
-            svh);
+    if (not obs.getObservations().empty())
+        satposs(obs.getObservations().front().time,
+                obs.data(),
+                obs.size(),
+                &nav.getNavigation(),
+                eph_opt,
+                rs,
+                dts,
+                var,
+                svh);
 
     // fill Satellites
     Satellites sats;