eina btlog - util - shut up coverity

eina_btlog is a backtrace "cleaner" that takes a raw bt from eina log
and gives a full readable bt for humans. it's run-and-quit binary like
ls or rm - it does its job and exits, so leaks are really of no
concern here...

CID 1297407

src/bin/eina/eina_btlog.c

@@ -154,6 +154,7 @@ bt_append(Eina_List *btl, const char *btline)
           }
         btl = eina_list_append(btl, bt);
      }
+   else free(bt);
    free(bin);
    return btl;
 }