Suppress macholib header parse error

Macholib raises ValueError when failing to parse files which can be used
to detect if the file is a Mach-O object.
It is also raised on Mach-O objects it doesn't know how to handle.

Checking for this error means `_is_macho_file` is redundant.

Changelog.md

@@ -34,6 +34,10 @@ rules on making a good Changelog.
 - `delocate-merge` now supports libraries with missing or unusual extensions.
   [#228](https://github.com/matthew-brett/delocate/issues/228)
 - Now supports library files ending in parentheses.
+- Fixed `Unknown Mach-O header` error when encountering a fat static library.
+  These files will be ignored until
+  [macholib](https://github.com/ronaldoussoren/macholib) supports them.
+  [#229](https://github.com/matthew-brett/delocate/issues/229)
 
 ### Removed
 

delocate/delocating.py

@@ -40,7 +40,6 @@
 from .pkginfo import read_pkg_info, write_pkg_info
 from .tmpdirs import TemporaryDirectory
 from .tools import (
-    _is_macho_file,
     _remove_absolute_rpaths,
     dir2zip,
     find_package_dirs,
@@ -599,9 +598,16 @@ def _get_macos_min_version(dylib_path: Path) -> Iterator[tuple[str, Version]]:
     Version
         The minimum macOS version.
     """
-    if not _is_macho_file(dylib_path):
-        return
-    for header in MachO(dylib_path).headers:
+    try:
+        macho = MachO(dylib_path)
+    except ValueError as exc:
+        if str(exc.args[0]).startswith(
+            ("Unknown fat header magic", "Unknown Mach-O header")
+        ):
+            return  # Not a recognised Mach-O object file
+        raise  # Unexpected error
+
+    for header in macho.headers:
         for cmd in header.commands:
             if cmd[0].cmd == LC_BUILD_VERSION:
                 version = cmd[1].minos
@@ -798,6 +804,8 @@ def _calculate_minimum_wheel_name(
     all_library_versions: dict[str, dict[Version, list[Path]]] = {}
 
     for lib in wheel_dir.glob("**/*"):
+        if lib.is_dir():
+            continue
         for arch, version in _get_macos_min_version(lib):
             all_library_versions.setdefault(arch.lower(), {}).setdefault(
                 version, []