wallet: free sql statement in wallet_onchaind_channels.

This is the cause of 'sqlite3_close: unable to close due to unfinalized statements or unfinished backups' with the --daemon option.

Fixes: #1420
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

wallet/wallet.c

@@ -2264,6 +2264,7 @@ u32 *wallet_onchaind_channels(struct wallet *w,
 		tal_resize(&channel_ids, count);
 			channel_ids[count-1] = sqlite3_column_int64(stmt, 0);
 	}
+	sqlite3_finalize(stmt);
 
 	return channel_ids;
 }