db: Track whether a db_stmt has been executed

For some of the query methods in the next step we need to have an idea of
whether the stmt was executed (db_step function) so let's track that
explicitly.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

wallet/db.c

@@ -593,6 +593,7 @@ struct db_stmt *db_prepare_v2_(const char *location, struct db *db,
 	stmt->location = location;
 	stmt->error = NULL;
 	stmt->db = db;
+	stmt->executed = false;
 	stmt->inner_stmt = NULL;
 
 	tal_add_destructor(stmt, db_stmt_free);
@@ -1346,6 +1347,7 @@ bool db_exec_prepared_v2(struct db_stmt *stmt TAKES)
 {
 	const char *expanded_sql;
 	bool ret = stmt->db->config->exec_fn(stmt);
+	stmt->executed = true;
 	if (stmt->db->config->expand_fn != NULL && ret &&
 	    !stmt->query->readonly) {
 		expanded_sql = stmt->db->config->expand_fn(stmt);

wallet/db_common.h

@@ -78,6 +78,8 @@ struct db_stmt {
 
 	/* Pointer to DB-specific statement. */
 	void *inner_stmt;
+
+	bool executed;
 };
 
 struct db_config {