Add a test that checks `get_route` and `uncertainty_update` behaviour's
handling of missing channel capacities.
Signed-off-by: Lagrang3 <lagrang3@protonmail.com>
The route-builder checks the liquidity bounds of each route one at a
time. Every route that satisfy the contraints is recorded in the
uncertainty network and produces an HTLC burden on the channels it uses,
so that the following routes cannot count on the same liquidity twice.
