Resolve crash on inventory pickup

[jengelh]

Commit d185ab951418a08383e5c7cc60d12339d404f57c broke the pointer-moving logic. When the allweapons cheat is executed or when e.g. the afterburner is picked up, ASAN terminates the program with:

==8330==ERROR: AddressSanitizer: heap-use-after-free on address 0x50f00007ab60
at pc 0x7f23334f6843 bp 0x7ffe724d2b10 sp 0x7ffe724d22d0
READ of size 3 at 0x50f00007ab60 thread T0
    f0 strdup
    f1 Inventory::AddCounterMeasure(int, int, int, int, char const*) Descent3/Inventory.cpp:575
    f2 Inventory::Add(int, int, object*, int, int, int, char const*) Descent3/Inventory.cpp:520
    f3 DemoCheats(int) Descent3/GameCheat.cpp:606
    f4 ProcessKeys() Descent3/GameLoop.cpp:2420
    f5 GameFrame() Descent3/GameLoop.cpp:2956
    f6 GameSequencer() Descent3/gamesequence.cpp:1212
    f7 PlayGame() Descent3/game.cpp:826
    f8 MainLoop() Descent3/descent.cpp:554
    f9 Descent3() Descent3/descent.cpp:507
    f10 oeD3LnxApp::run() Descent3/sdlmain.cpp:142
    f11 main Descent3/sdlmain.cpp:323

0x50f00007ab60 is located 0 bytes inside of 175-byte region [0x50f00007ab60,0x50f00007ac0f)
freed by thread T0 here:
    f1 mng_LoadNetGenericPage(CFILE*, bool) manage/generic.cpp:2216
    f2 mng_LoadNetPages(int) manage/manage.cpp:1281
    f3 mng_LoadTableFiles(int) manage/manage.cpp:648
    f4 InitD3Systems2(bool) Descent3/init.cpp:1891
    f5 Descent3() Descent3/descent.cpp:503
    f6 oeD3LnxApp::run() Descent3/sdlmain.cpp:142
    f7 main Descent3/sdlmain.cpp:323

previously allocated by thread T0 here:
    f0 malloc
    f1 mem_rmalloc<char> mem/mem.h:138
    f2 mng_ReadNewGenericPage(CFILE*, mngs_generic_page*) manage/generic.cpp:1145
    f3 mng_LoadNetGenericPage(CFILE*, bool) manage/generic.cpp:2196
    f4 mng_LoadNetPages(int) manage/manage.cpp:1281
    f5 mng_LoadTableFiles(int) manage/manage.cpp:648
    f6 InitD3Systems2(bool) Descent3/init.cpp:1891
    f7 Descent3() Descent3/descent.cpp:503
    f8 oeD3LnxApp::run() Descent3/sdlmain.cpp:142
    f9 main Descent3/sdlmain.cpp:323

The pointer value of mngs_generic_page::description was copied to object_info::description (by function mng_AssignGenericPageToObjInfo) and then the page was freed in mng_LoadNetGenericPage, leaving object_info::description non-NULL and dangling.

Fixes: d185ab951418a08383e5c7cc60d12339d404f57c

Pull Request Type

• [x] Runtime changes
  • [x] Other changes

Checklist

• [x] I have tested my changes locally and verified that they work as intended.
• [x] I have reviewed the changes to ensure they do not introduce any unnecessary complexity or duplicate code.
• [x] I understand that by submitting this pull request, I am agreeing to license my contributions under the project's license.