calc-moon: Prefer g_auto* macros

g_autofree will automatically free variables when they go out of
scope. g_autoptr will do the same, but using the appropriate freefunc
for the given type, e.g. GDateTime -> g_date_time_unref() or
GObject -> g_object_unref().

This automatic cleanup reduces the risk of memory leaks
and allows getting rid of some lines of code.

src/calculations/calculations_moon.c

@@ -68,8 +68,8 @@ picplanner_get_illumination (GDateTime *date_time)
 {
   double illumination;
   double elongation;
-  double *coordinates_moon;
-  double *coordinates_sun;
+  g_autofree double *coordinates_moon = NULL;
+  g_autofree double *coordinates_sun = NULL;
   double ra_sun, dec_sun, ra_moon, dec_moon;
   coordinates_moon = picplanner_get_coordinates_rotational_moon (date_time);
   coordinates_sun = picplanner_get_coordinates_rotational_sun (date_time);
@@ -82,9 +82,6 @@ picplanner_get_illumination (GDateTime *date_time)
   elongation = sin(dec_sun)*sin(dec_moon) + cos(dec_sun)*cos(dec_moon)*cos(ra_sun-ra_moon);
   illumination = (1 - elongation)/2;
 
-  g_free (coordinates_moon);
-  g_free (coordinates_sun);
-
   return illumination*100.;
 }
 
@@ -95,7 +92,7 @@ double
                                   double    latitude)
 {
   double siderial_time;
-  double *coordinates_moon;
+  g_autofree double *coordinates_moon = NULL;
   double *coordinates_horizontal_moon;
 
   coordinates_moon = picplanner_get_coordinates_rotational_moon (date_time);
@@ -104,7 +101,6 @@ double
                                                                                latitude,
                                                                                siderial_time);
 
-  g_free (coordinates_moon);
 
   return coordinates_horizontal_moon;
 }
@@ -115,22 +111,19 @@ double
                                         double    longitude,
                                         double    latitude)
 {
-  GDateTime *iteration_time;
-  double *coordinates_moon;
   double *array_coordinates_moon = malloc (sizeof (double) * 2 * NUM_DATA_POINTS);
 
   for (int i=0; i<NUM_DATA_POINTS; i++)
     {
-      iteration_time = g_date_time_add_minutes (date_time, i*24*60/NUM_DATA_POINTS-12*60);
-
-      coordinates_moon = picplanner_get_coordinates_moon (iteration_time,
+      g_autoptr (GDateTime) iteration_time =
+	g_date_time_add_minutes (date_time, i*24*60/NUM_DATA_POINTS-12*60);
+      g_autofree double *coordinates_moon =
+	picplanner_get_coordinates_moon (iteration_time,
 					 longitude,
 					 latitude);
+
       array_coordinates_moon[2*i] = coordinates_moon[0];
       array_coordinates_moon[2*i+1] = coordinates_moon[1];
-
-      g_free (coordinates_moon);
-      g_date_time_unref (iteration_time);
     }
 
   return array_coordinates_moon;