Fix pointer dereferencing

Setting the pointer to NULL had no effect outside the function so far.

src/config/preferences.c

@@ -203,7 +203,6 @@ prefs_free_string(char *pref)
     if (pref) {
         g_free(pref);
     }
-    pref = NULL;
 }
 
 

src/muc.c

@@ -976,6 +976,5 @@ _occupant_free(Occupant *occupant)
         free(occupant->jid);
         free(occupant->status);
         free(occupant);
-        occupant = NULL;
     }
 }

src/ui/buffer.c

@@ -76,7 +76,6 @@ buffer_free(ProfBuff buffer)
 {
     g_slist_free_full(buffer->entries, (GDestroyNotify)_free_entry);
     free(buffer);
-    buffer = NULL;
 }
 
 void