sql: do not increase row-count if INSERT OR IGNORE fails

If INSERT statement is executed with IGNORE error action (i.e.
INSERT OR IGNORE ...), it will return number of rows inserted.
For example:

CREATE TABLE t (i INT PRIMARY KEY, a INT check (a > 0));
INSERT OR IGNORE INTO t VALUES (1, 1), (2, -1), (3, 2);

Should return:
---
- row_count: 2
...

However it was three before this patch. So, let's account number
of successful insertions in case of INSERT OR IGNORE.

Follow-up #4188