Avoidable rectangle is applied even if there is no double solution

[Kermalis]

The following puzzle (currently named Unsolved - Incorrect 1.txt in the repo):

1549-----
-----41--
-6-75---9
-1---8---
69---7-4-
--5----37
-8-----1-
----3--68
------5--

Avoidable rectangle is applied (because other techniques are not implemented yet)
For now, it points out a flaw with my implementation of avoidable rectangle.

G4 should not be changed because G7 cannot be 6 and D7 cannot be 3. This means a double solution involving G4 is not possible, so the avoidable rectangle should not try to avoid it.

The technique needs to check if it would be a double solution if the three cells were swapped.

[Kermalis]

This puzzle is now solved by XY-Chain, but the bug still applies if XY-Chain is disabled. It was renamed to XY-Chain (2).txt