Core/maps: Forgot to include the optional "active" parameter to PlanetHistory.load()

Signed-off-by: Martin Stone <martin@d7415.co.uk>
(cherry picked from commit 6d9ca8c7971ef4500f5aed7aec894fa3b15d3ab6)
parser: Handle missing planets.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
(cherry picked from commit 0ede533f49f9fa61140968e3988e6a3805874be2)