Re: BUG #18984: Empty prepared statement from psql \parse triggers assert in PortalRunMulti

Hi,

> That being the case, maybe we should band-aid this by returning
> EXECUTE if the prepared statement is empty.

This sounds pretty straightforward and seems to solve the problem.
Patch attached.

```
eax=# \parse s
eax=# execute s;
ERROR:  EXECUTE can't execute an empty query
eax=# select 1 \parse s2

eax=# execute s2;
 ?column?
----------
        1
(1 row)
```