Crash on bad MHMAT link

[joepal1976]

It's an edge case, but in case you installed a corrupt asset where the MHCLO points at a non-existing MHMAT, you get an ugly crash:

[CRASH] ui.new_human.randomize.createrandomhuman : Execution caused an exception 

An unhandled error was encountered. Please provide this info in an error report:

CONTEXT
-------
context .............. : <bpy_struct, Context at 0x7d35ade865c8>
scene ................ : <bpy_struct, Scene("Scene") at 0x7d332acf00a0>
active_object ........ : <bpy_struct, Object("Human.sssnake_starship_uniform_green_capt_shirt") at 0x7d353f165608>
active_object_mode ... : OBJECT
active_object_type ... : Clothes

OPERATOR
--------
name ................. : MPFB_OT_create_random_human
label...... .......... : Create random human

SYSTEM
------
blender_version ...... : (5, 1, 0)
blender_version_string : 5.1.0
python_version ....... : 3.13.9 (main, Apr 25 2025, 12:39:20) [GCC 14.2.1 20250110 (Red Hat 14.2.1-7)]
platform ............. : Linux-6.8.0-136-generic-x86_64-with-glibc2.39
platform system....... : Linux
platform release...... : 6.8.0-136-generic

MPFB
----
version .............. : (2, 0, 17)
build ................ : FROM_SOURCE
data dir ............. : /home/joepal/raspberry/mpfb2/src/mpfb/data
mpfb dir ............. : /home/joepal/raspberry/mpfb2/src/mpfb
user dir ............. : /home/joepal/makehuman/mpfb

ERROR
-----
type ................. : FileNotFoundError
message .............. : [Errno 2] No such file or directory: '/home/joepal/makehuman/mpfb/data/clothes/sssnake_starship_uniform_green_capt_shirt/starship_uniform.mhmat'

STACK TRACE
-----------
Traceback (most recent call last):
  File "/home/joepal/source/blender-extensions/repo/mpfb/ui/mpfboperator.py", line 110, in execute
    return self.hardened_execute(context)
           ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
  File "/home/joepal/source/blender-extensions/repo/mpfb/ui/new_human/randomize/operators/createrandomhuman.py", line 50, in hardened_execute
    basemesh = characterbuilder.build_character(spec, macro_details, rng, self.report, discovery)
  File "/home/joepal/source/blender-extensions/repo/mpfb/ui/new_human/randomize/characterbuilder.py", line 163, in build_character
    _apply_random_clothes(report, spec, macro_details, basemesh, rng, discovery, subdiv_levels)
    ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/joepal/source/blender-extensions/repo/mpfb/ui/new_human/randomize/characterbuilder.py", line 400, in _apply_random_clothes
    HumanService.add_mhclo_asset(pick["path"], basemesh, asset_type="Clothes", subdiv_levels=subdiv_levels,
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                                 material_type=material_type)
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/joepal/source/blender-extensions/repo/mpfb/services/humanservice.py", line 565, in add_mhclo_asset
    makeskin_material.populate_from_mhmat(material)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
  File "/home/joepal/source/blender-extensions/repo/mpfb/entities/material/mhmaterial.py", line 79, in populate_from_mhmat
    with open(full_path, 'r') as f:
         ~~~~^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: '/home/joepal/makehuman/mpfb/data/clothes/sssnake_starship_uniform_green_capt_shirt/starship_uniform.mhmat'

Desired outcome is that there instead is an informative warning that the material could not be loaded.