Do not move into monsters that we cannot displace

[Qrox]

Summary

Bugfixes "Do not move into monsters that we cannot displace"

Purpose of change

When you are on a fence and moves into a friendly monster that cannot move onto the fence, the player moves into the monster anyway and occupies the same space as the monster.

Describe the solution

Return the original player position from game::place_player if the monster cannot be moved, so both the monster and the player are not moved.
To get past the string freeze, an existing string is used for the message when the monster fails to move.

Testing

Climb onto a fence and tried to move into a nearby monster. The player did not move and a message was shown.