[Bug]: Company HQ can be rebuilt in the exact same location

[James103]

Version of OpenTTD

Since #8510 on Windows 10, 64-bit (via Steam)

Expected result

A company's HQ should not be able to be relocated to the same exact location it already is in, or doing so should be free.
A company's HQ should still be relocatable one tile laterally and/or longitudinally, relative to the existing location.

Actual result

A company's HQ can be relocated to the same exact location it already is in, costing the same amount (1% of value) as relocating to another location.

Steps to reproduce

1. Build HQ.
2. Relocate HQ to the same exact location as the current HQ (by clicking the same tile).