Bug 797983 - v4.2 report numbers change over gnucash restarts;...

Price Database dropping user:price-editor entries.

A wider problem: QofInstance was unmarking itself dirty as long as the
backend raised an error and unconditionally marking itself non-infant.

This matters because the SQL backend depends on infant status to decide
whether to do an insert or update query; either will fail if the infant
status is wrong.

The price editor dialog clones a price having only its commodity set and
GncSqlPriceBackend declines to save if the currency isn't set. Since the
instance marked itself non-infant even though it wasn't saved subsequent
commits tried to use an update query and since the price wasn't in the
table that inevitably failed.

Requiring that QofBackend::commit should doing the marking-clean
required implementing it in the backends where it wasn't already.

libgnucash/engine/qof-backend.cpp

@@ -48,6 +48,13 @@ G_GNUC_UNUSED static QofLogModule log_module = QOF_MOD_BACKEND;
 
 GModuleVec QofBackend::c_be_registry{};
 
+void
+QofBackend::commit(QofInstance* instance)
+{
+    if (qof_instance_is_dirty(instance))
+        qof_instance_mark_clean(instance);
+}
+
 void
 QofBackend::set_error(QofBackendError err)
 {