[IMP] util/pg: skip None counts when summing

[cr.rowcount](https://www.psycopg.org/docs/cursor.html#cursor.rowcount)
may start (at some non-disclosed point) to return `None` instead of `-1`.

Which would cause the following error:

```python
TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'
```

Part-of: #49

Author: Pirols

src/util/pg.py

@@ -118,7 +118,7 @@ def execute(query):
                 log_hundred_percent=True,
             ):
                 try:
-                    tot_cnt += future.result()
+                    tot_cnt += future.result() or 0
                 except psycopg2.OperationalError as exc:
                     if exc.pgcode not in CONCURRENCY_ERRORCODES:
                         raise