Prevent segfault when deconstructing improvised shelter

[inogenous]

Summary

Bugfixes "Prevent segfault when deconstructing improvised shelter"

Purpose of change

Fixes #75525 .

Describe the solution

Previous segfault happened when trying to display the list of items that deconstruction would yield, but this terrain has no deconstruct json.

This commit also adds a check with debugmsg for future such cases during the game startup validation. It also fixes other terrains that had the same problem (t_improvised_shelter_filled, t_rockyobstacle and t_carpet_concrete_green_olight).

Previous crash being fixed:

Thread 1 "cataclysm-tiles" received signal SIGSEGV, Segmentation fault.
0x0000555555cb9602 in operator() (drop_group=..., __closure=<optimized out>) at src/construction.cpp:2049
2049                            item_group::spawn_data_from_group( drop_group )->every_item_min_max();
(gdb) bt
 #0  0x0000555555cb9602 in operator() (drop_group=..., __closure=<optimized out>) at src/construction.cpp:2049
 #1  0x0000555555cb9af2 in construct::do_turn_deconstruct (p=..., who=...) at src/construction.cpp:2086
 #2  0x0000555555a32fad in activity_handlers::build_do_turn (act=0x5555583e4338, you=0x5555583e3c70) at src/activity_handlers.cpp:3424
 #3  0x0000555555a6b7de in std::function<void(player_activity*, Character*)>::operator() (this=<optimized out>, __args#0=<optimized out>, __args#0@entry=0x5555583e4338, __args#1=<optimized out>, __args#1@entry=0x5555583e3c70) at /usr/include/c++/14/bits/std_function.h:591
 #4  0x0000555555a69647 in activity_type::call_do_turn (this=<optimized out>, act=act@entry=0x5555583e4338, you=you@entry=0x5555583e3c70) at src/activity_type.cpp:160
 #5  0x00005555566d3a1c in player_activity::do_turn (this=0x5555583e4338, you=...) at src/player_activity.cpp:320
 #6  0x0000555555dcef82 in do_turn () at src/do_turn.cpp:592
 #7  0x00005555557a1217 in main (argc=<optimized out>, argv=<optimized out>) at src/main.cpp:873

Describe alternatives you've considered

Considered just removing the EASY_DECONSTRUCT flag from the improvised shelters, but that would have been too easy.

Testing

Can no longer reproduce the segfault in #75525 . The improvised shelter can now be simple-deconstructed:

Additional context