Protect Gswe*Data from NULL pointers

src/gswe-antiscion-data.c

@@ -220,6 +220,10 @@ gswe_antiscion_data_ref(GsweAntiscionData *antiscion_data)
 void
 gswe_antiscion_data_unref(GsweAntiscionData *antiscion_data)
 {
+    if (antiscion_data == NULL) {
+        return;
+    }
+
     if (--antiscion_data->refcount == 0) {
         gswe_antiscion_data_free(antiscion_data);
     }

src/gswe-aspect-data.c

@@ -203,6 +203,10 @@ gswe_aspect_data_ref(GsweAspectData *aspect_data)
 void
 gswe_aspect_data_unref(GsweAspectData *aspect_data)
 {
+    if (aspect_data == NULL) {
+        return;
+    }
+
     if (--aspect_data->refcount == 0) {
         gswe_aspect_data_free(aspect_data);
     }

src/gswe-moon-phase-data.c

@@ -88,6 +88,10 @@ gswe_moon_phase_data_ref(GsweMoonPhaseData *moon_phase_data)
 void
 gswe_moon_phase_data_unref(GsweMoonPhaseData *moon_phase_data)
 {
+    if (moon_phase_data == NULL) {
+        return;
+    }
+
     if (--moon_phase_data->refcount == 0) {
         g_free(moon_phase_data);
     }

src/gswe-planet-data.c

@@ -99,6 +99,10 @@ gswe_planet_data_ref(GswePlanetData *planet_data)
 void
 gswe_planet_data_unref(GswePlanetData *planet_data)
 {
+    if (planet_data == NULL) {
+        return;
+    }
+
     if (--planet_data->refcount == 0) {
         gswe_planet_data_free(planet_data);
     }