[Fix] Wasn't freeing sound properly.

dat/planet.xml

@@ -23,7 +23,7 @@
     <main>3</main>
    </tech>
    <services>31</services>
-   <class>A</class>
+   <class>M</class>
   </general>
  </planet>
  <planet name="New Haven">

src/sound.c

@@ -78,10 +78,10 @@ void sound_exit(void) {
   int i;
   
   /* Free the sounds. */
-  sound_free(&sound_list[i]);
+  for(i = 0; i < sound_nlist; i++)
+    sound_free(&sound_list[i]);
   free(sound_list);
   sound_list = NULL;
-
   sound_nlist = 0;
 
   music_exit();