A cached query planned statement contains information that is
freed after the first execution of a function. The second execution
used the cached planned statement to populate the execution state
using a freed pointer and throws a segmentation fault.

To resolve, we copy the contents out of the planned statement rather
than copying a pointer to the planned statement, so that when our
executor state gets freed, it does not also free the cached data.

Note: `numSelectorsPerScanId` is the problematic property, and is only
used for partition tables.
Co-authored-by: NDavid Kimura <dkimura@pivotal.io>
Co-authored-by: NTaylor Vesely <tvesely@pivotal.io>