Fix sacrifice recipe qsort comparator

[NeptixFTW]

Summary

Fixes #4703 by replacing the sacrifice-recipe qsort comparator with one that satisfies the C comparator contract and keeps unused zero victim slots after valid creature models.

Root cause

qsort requires its comparator to return a negative value when the first element sorts before the second, zero for equal elements, and a positive value when it sorts after the second. The previous comparator returned the boolean expression a < b, so it returned only 0 or 1: unequal values could be reported as equal, and ascending values could be reported in the wrong direction.

The resulting behavior is runtime-dependent because different C library qsort implementations compare and partition elements differently. The Amiga runtime exposes the shipped CHEAPER_IMPS failure and logs Found unsupported CHEAPER_IMPS sacrifice. The Windows runtime used for testing masks that particular failure: unpatched master happened to retain the shipped one-IMP recipe as [IMP, 0, ...], so the warning was not emitted and the price effect still worked, despite the comparator being invalid.

Validation

• Reproduced the invalid comparator on exact unpatched master with a temporary KeeperFX functional test. It returned zero/imp=1, imp/zero=0, lower/higher=1, higher/lower=0, and the test failed with exit code -1.
• Ran the same functional test with this fix. It returned valid comparator signs (1, -1, -1, 1, and 0 for equality), parsed the CHEAPER_IMPS recipe as IMP model 23 followed by zero slots, increased cheaper_diggers from 0 to 1, and reduced the create-imp price from 600 to 450. The test passed with exit code 0.
• Built the fixed executable with the repository-supported i686 MinGW CMake configuration.
• Launched the fixed executable successfully, reached the main menu, and loaded original Dungeon Keeper campaign level 1.

The temporary functional-test harness and development game copy are not included in this change.