Prevent segfault in expand_tuple with no missing values

Andrew Dunstan <andrew@dunslane.net>

Commit: 7c44c46deb495a2f3861f402d7f2109263e3d50a
Author: Andrew Dunstan <andrew@dunslane.net>
Date: 2018-04-13T20:43:33Z
Releases: 11.0
Prevent segfault in expand_tuple with no missing values

Commit 16828d5c forgot to check that it had a set of missing values
before trying to retrieve a value from it.

An additional query to add coverage for this code is added to the
regression test.

Per bug report from Andreas Seltenreich.

Files