Fix uniqueColors comparator strict weak ordering

[qwe854896]

Fix an issue in the uniqueColors sorting comparator where the use of <= violated the requirements of a strict weak ordering. The comparison now uses < instead to restore correct comparator behavior and prevent undefined behavior during sorting.

In terms of the algorithm's contract, the comparator used by std::sort must induce a strict weak ordering. In particular:

• For all a, comp(a, a) == false.
• If comp(a, b) == true then comp(b, a) == false.

Using <= violated these rules when two elements were equal. Replacing <= with < ensures compliance with the standard and improves stability.

Even if equal QColor are unlikely or impossible to appear in uniqueColors, switching to < is still safe and makes the comparator correct by definition. If QColor can never be equal, then < and <= behave the same anyway.

References:

• C++ reference, C++ named requirements: Compare

[ddennedy]

Thank you