Allow insert-multi! with empty list of rows

[seancorfield]

Is your feature request related to a problem? Please describe.
If you are programmatically generating the list of rows to insert, you may have an empty list. This causes insert-multi! to fail.

Describe the solution you'd like
insert-multi! should treat an empty list of rows as a no-op.

Describe alternatives you've considered
Users would need to check the list of rows and only call insert-multi! if it is non-empty but this will require holding on to the head of the list.

Additional context
Some functions already require non-empty data structures -- the ::example-map used for find-by-keys, update!, and delete! are examples.