Although we check for valid coordinates in the table plugin via
`check_all_coordinates`, we do not check for #srcs > 0 and #dsts > 0.
This would be fine as the grammar parser combines adding coordinates and
setting their `is_source` and `is_destination` property, which makes
adding coordinates without specifying source or destination impossible.
See: route_parameters.cpp, AddSource, AddDestination, and api_grammar.hpp
In contract, the Polyline codepath does not do this! In fact, it only lets
you set coordinates, but not their `is_source` or `is_destination` property.
See: route_parameters.cpp, SetCoordinatesFromGeometry
Therefore, the following queries only set coordinates:
http 'http://localhost:5000/table?locs=s_hhFg{arEgEfEgEfEgEfEgEfEgEfEgEfEgEfEgEfEgEfE'
http 'http://localhost:5000/table?locs=_p~iF~ps|U_ulLnnqC_mqNvxq`@'
but fail to specify sources and targets!
The distance table plugin now assumes `is_course` and `is_destination`
is the same size as `coordinates`.
And happily accesses uninitialized memory.
