fix: generate-inx-files failing with Nix

Fixes the following error when attempting to build the Nix package:

    python bin/generate-inx-files;
    Traceback (most recent call last):
      File "/build/inkstitch/bin/generate-inx-files", line 59, in <module>
        from lib.inx.generate import generate_inx_files
      File "/build/inkstitch/lib/inx/generate.py", line 6, in <module>
        from .extensions import generate_extension_inx_files
      File "/build/inkstitch/lib/inx/extensions.py", line 10, in <module>
        from ..commands import (COMMANDS, GLOBAL_COMMANDS, LAYER_COMMANDS,
      File "/build/inkstitch/lib/commands.py", line 16, in <module>
        from .i18n import N_, _
      File "/build/inkstitch/lib/i18n.py", line 10, in <module>
        from .utils import cache, get_resource_dir
      File "/build/inkstitch/lib/utils/__init__.py", line 6, in <module>
        from . import cache as cache_module  # Slight hack to allow cache to be imported for monkeypatching
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/build/inkstitch/lib/utils/cache.py", line 13, in <module>
        from lib.utils.settings import global_settings
      File "/build/inkstitch/lib/utils/settings.py", line 84, in <module>
        global_settings = GlobalSettings()
                          ^^^^^^^^^^^^^^^^
      File "/build/inkstitch/lib/utils/settings.py", line 48, in __init__
        self.__settings_file = os.path.join(get_user_dir(), "settings.json")
                                            ^^^^^^^^^^^^^^
      File "/build/inkstitch/lib/utils/paths.py", line 50, in get_user_dir
        os.makedirs(path)
      File "<frozen os>", line 215, in makedirs
      File "<frozen os>", line 215, in makedirs
      File "<frozen os>", line 225, in makedirs
    PermissionError: [Errno 13] Permission denied: '/homeless-shelter'

lib/utils/paths.py

@@ -41,12 +41,12 @@ def get_resource_dir(name):
         return realpath(os.path.join(dirname(realpath(__file__)), '..', '..', name))
 
 
-def get_user_dir(name=None):
+def get_user_dir(name=None, create=True):
     try:
         path = platformdirs.user_config_dir('inkstitch')
     except ImportError:
         path = os.path.expanduser('~/.inkstitch')
-    if not os.path.exists(path):
+    if create and not os.path.exists(path):
         os.makedirs(path)
 
     if name is not None:

lib/utils/settings.py

@@ -45,7 +45,11 @@ DEFAULT_SETTINGS = {
 class GlobalSettings(MutableMapping):
     def __init__(self):
         super().__init__()
-        self.__settings_file = os.path.join(get_user_dir(), "settings.json")
+        # We set create=False here because this code is executed on module load
+        # and via imports also runs on generate-inx-files, which with the Nix
+        # package manager is executed with a non-writable home directory.
+        user_dir = get_user_dir(create=False)
+        self.__settings_file = os.path.join(user_dir, "settings.json")
         self.__settings = {}
 
         for name, value in DEFAULT_METADATA.items():