Fail gracefully if config lacks the mandatory main section

Currently, if a user didn't put `[general]` section in config file,
bugwarrior fails like this:

    Traceback (most recent call last):
      File "/usr/bin/bugwarrior", line 8, in <module>
        sys.exit(cli())
                 ~~~^^
      File "/usr/lib/python3.14/site-packages/click/core.py", line 1485, in __call__
        return self.main(*args, **kwargs)
               ~~~~~~~~~^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.14/site-packages/click/core.py", line 1406, in main
        rv = self.invoke(ctx)
      File "/usr/lib/python3.14/site-packages/click/core.py", line 1873, in invoke
        return _process_result(sub_ctx.command.invoke(sub_ctx))
                               ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
      File "/usr/lib/python3.14/site-packages/click/core.py", line 1269, in invoke
        return ctx.invoke(self.callback, **ctx.params)
               ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.14/site-packages/click/core.py", line 824, in invoke
        return callback(*args, **kwargs)
      File "/usr/lib/python3.14/site-packages/click/decorators.py", line 34, in new_func
        return f(get_current_context(), *args, **kwargs)
      File "/usr/lib/python3.14/site-packages/bugwarrior/command.py", line 62, in wrapped_subcommand_callback
        return ctx.invoke(subcommand_callback, *args, **kwargs)
               ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.14/site-packages/click/core.py", line 824, in invoke
        return callback(*args, **kwargs)
      File "/usr/lib/python3.14/site-packages/bugwarrior/command.py", line 105, in pull
        config = _try_load_config(main_section, interactive, quiet)
      File "/usr/lib/python3.14/site-packages/bugwarrior/command.py", line 35, in _try_load_config
        return load_config(main_section, interactive, quiet)
      File "/usr/lib/python3.14/site-packages/bugwarrior/config/load.py", line 122, in load_config
        rawconfig['flavor'][main_section]['interactive'] = interactive
        ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
    KeyError: 'general'

This is confusing — it looks more like bugwarrior broke due to some
API change in Python, rather than because of a user mistake.

So handle this case with explicit check. Now it will fail instead like
this:

    Validation error found in /home/constantine/.config/bugwarrior/bugwarriorrc
    See https://bugwarrior.readthedocs.io

    No section: 'general'

Author: Hi-Angel

bugwarrior/config/load.py

@@ -119,7 +119,9 @@ def parse_file(configpath: str) -> dict:
 def load_config(main_section, interactive, quiet) -> Config:
     configpath = get_config_path()
     rawconfig = parse_file(configpath)
-    rawconfig['flavor'][main_section]['interactive'] = interactive
+    for section in rawconfig['flavor']:
+        if isinstance(section, dict):
+            section['interactive'] = interactive
     config = validate_config(rawconfig, main_section, configpath)
     configure_logging(
         config.main.log_file, 'WARNING' if quiet else config.main.log_level

tests/config/test_load.py

@@ -262,3 +262,22 @@ def test_ini_wrong_prefix(self):
 
         with self.assertRaises(SystemExit):
             load.parse_file(config_path)
+
+
+class TestLoadConfig(LoadTest):
+    def test_main_section_does_not_exist(self):
+        config_path = self.create(".bugwarriorrc")
+        with open(config_path, 'w') as fout:
+            fout.write(
+                textwrap.dedent("""
+                [redmine]
+                service = redmine
+                redmine.url = example.com
+            """)
+            )
+
+        with self.assertRaises(SystemExit):
+            load.load_config("general", False, False)
+
+        self.assertEqual(len(self.caplog.records), 1)
+        self.assertIn("No section: 'general'", self.caplog.records[0].message)