bugfix(saveload): Restore dock approach position reached flags on load

[bobtista]

• Fixes Units queued at a dock never dock again after loading a save #3116

DockUpdate::xfer reads each m_approachPositionReached entry into a local Bool and passes its address to xferBool. BoolVector is std::vector<bool>, whose operator[] returns a proxy rather than a reference, so on load the value is written into the local and discarded and the vector keeps the false entries left by resize(). m_approachPositionOwners is restored correctly, so after loading the dock still holds its approach slots while every reached flag reads false. isClearToAdvance never returns true and DockUpdate::update never finds a position to promote to m_activeDocker, and the flags are only set by onApproachReached, which fires from AIDockApproachState::onExit and will not fire again for a unit that is already waiting.

Now the unpacked value is written back into the vector after the xfer, so the reached flags survive a save and load and the queue keeps running. This does not change the save layout, so existing saves still load.

Todo:

• Verify in skirmish: save with a worker docked and another queued, load, confirm the queued worker docks
• Replicate to Generals