mformat: provide nice error message instead of backtrace for invalid …

…value

I ran into this with `option = true;` (note the trailing `;`). Now we
provide a nicer message instead of an uncaught Python backtrace.

Closes: mesonbuild#13565

mesonbuild/mformat.py

@@ -861,7 +861,11 @@ def load_configuration(self, configuration_file: T.Optional[Path]) -> FormatterC
 
  for f in fields(config):
  getter = f.metadata['getter']
- value = getter(cp, cp.default_section, f.name, fallback=None)
+ try:
+ value = getter(cp, cp.default_section, f.name, fallback=None)
+ except ValueError as e:
+ raise MesonException(
+ f'Error parsing "{str(configuration_file)}", option "{f.name}", error: "{e!s}"')
  if value is not None:
  setattr(config, f.name, value)