bug fixed and RTKLIB version

RTKLIB @ 4ab9a199

-Subproject commit 0260d91932df0ca0691842aa99b39acde5d49c45
+Subproject commit 4ab9a199ff46b1220fb4fe99b019c8df526e53e9

src/utils/satellite.cpp

@@ -47,15 +47,16 @@ 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;