Fix loading status in 2 progress bars

Increment tiles_done in clearInvalidHouseTiles and
clearModifiedTileState.
Fix pos_retries bug

This commit also removes an unnecessary check
Fix potential null pointer dereferencing

SendNode assumes that the node pointer passed to it isn't nullptr, and
createLeaf can return nullptr, so this commit prevents the map editor
from crashing if that happens.
Virtual deconstructor for ActionQueue

ActionQueue is being inherited inherited from NetworkActionQueue, so the
deconstructor of ActionQueue should be declared virtual to make sure all
deconstructors that should be called are called.
Fix wrong use of std::remove and std::unique

std::remove(begin, end, value) and std::unique don't actually erase
anything, they return a new iterator which is meant to be the new end,
and everything between that and the actual end should be erased.
Fix wrong use of std::shared_ptr

Memory allocated with new[] should be free'd using delete[], the default
behavior of shared ptr is to free memory using delete.
Small optimization

n - amount > 0 for unsigned values should be the same as n != amount
Fix screenshot path bug
Remove unused variables
Return null instead of false, OnAcceptConnection

The function returns a pointer, not a boolean.
Remove redundant if-statement