Fix a crash with hardened_malloc

Palapeli crashed when starting with the backtrace below and
hardened_malloc complaining about "fatal allocator error: sized
deallocation mismatch (small)".

 #0  0x00007ffff5cbe16c in __pthread_kill_implementation () from /usr/x86_64-pc-linux-gnu/lib/libc.so.6
 #1  0x00007ffff5c6eb36 in raise () from /usr/x86_64-pc-linux-gnu/lib/libc.so.6
 #2  0x00007ffff5c57835 in abort () from /usr/x86_64-pc-linux-gnu/lib/libc.so.6
 #3  0x00007ffff7fb90e9 in fatal_error () from /usr/x86_64-pc-linux-gnu/lib/libhardened_malloc-light.so
 #4  0x00007ffff7fb9233 in deallocate_small[cold] () from /usr/x86_64-pc-linux-gnu/lib/libhardened_malloc-light.so
 #5  0x00007ffff7fbc2c0 in free_sized () from /usr/x86_64-pc-linux-gnu/lib/libhardened_malloc-light.so
 #6  0x00007ffff7fbcb8e in operator delete(void*, unsigned long) () from /usr/x86_64-pc-linux-gnu/lib/libhardened_malloc-light.so
 #7  0x00007ffff7f5ee99 in Pala::IntegerProperty::~IntegerProperty (this=<optimized out>, this=<optimized out>)
     at /var/tmp/paludis/build/kde-palapeli-scm/work/palapeli-scm/libpala/slicerproperty.cpp:169
 #8  0x00007ffff7f609b6 in qDeleteAll<QList<Pala::SlicerProperty const*>::const_iterator> (end=..., begin=...)
     at /usr/x86_64-pc-linux-gnu/include/qt6/QtCore/qalgorithms.h:27
 #9  qDeleteAll<QList<Pala::SlicerProperty const*> > (c=...) at /usr/x86_64-pc-linux-gnu/include/qt6/QtCore/qalgorithms.h:35
 #10 Pala::Slicer::~Slicer (this=<optimized out>, this=<optimized out>) at /var/tmp/paludis/build/kde-palapeli-scm/work/palapeli-scm/libpala/slicer.cpp:36
 #11 0x0000739689c5cba3 in GoldbergSlicer::~GoldbergSlicer (this=<optimized out>, this=<optimized out>)
     at /var/tmp/paludis/build/kde-palapeli-scm/work/palapeli-scm/slicers/goldberg/slicer-goldberg.h:16
 #12 GoldbergSlicer::~GoldbergSlicer (this=<optimized out>, this=<optimized out>)
     at /var/tmp/paludis/build/kde-palapeli-scm/work/palapeli-scm/slicers/goldberg/slicer-goldberg.h:16
 #13 0x00005555555bd1e5 in std::default_delete<Pala::Slicer>::operator() (__ptr=0x73c9a5b9fe70, this=<optimized out>)
     at /usr/x86_64-pc-linux-gnu/include/c++/13/bits/unique_ptr.h:93
 #14 std::unique_ptr<Pala::Slicer, std::default_delete<Pala::Slicer> >::~unique_ptr (this=<optimized out>, this=<optimized out>)
     at /usr/x86_64-pc-linux-gnu/include/c++/13/bits/unique_ptr.h:404

(cherry picked from commit 336cb4e7)