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

…value

I ran into this with `option = true;` (not the trailing `;`). Now we
provide a nicer message instead of an uncaught Python traceback.

Closes: mesonbuild#13565

mesonbuild/mformat.py

@@ -839,7 +839,13 @@ 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:
+                    value = str(e).split(':')[1].strip()
+                    raise MesonException(
+                        f'Error parsing "{str(configuration_file)}", option "{f.name}" '
+                        f'has invalid value: "{value}"')
                 if value is not None:
                     setattr(config, f.name, value)