Use a local instead of a temporary as an argument to valueOrDefault

[bshastry]

Fixes #11343

[ekpyron]

Hm... I wonder whether in CommonData.h we should change

	typename ValueType = std::decay_t<decltype(std::declval<MapType>().find(std::declval<KeyType>())->second)> const&,

to

	typename ValueType = std::decay_t<decltype(std::declval<MapType>().find(std::declval<KeyType>())->second)>,

instead...
(in the template arguments to valueOrDefault)

[ekpyron]

It's a bit tricky, though - we do want to avoid a copy there, if possible. I'd need to think about it... maybe we should also have it disallow this case without specifically passing allow_copy to it...

[ekpyron]

Approving this, since it'll work as fix, but we should rethink the behaviour of valueOrDefault in cases like this and make it safer.