Report an unreadable sysdiagnose archive instead of aborting silently (#920)

A sysdiagnose tarball whose download stopped halfway ends in an EOFError
from gzip while check-sysdiagnose extracts it. Click turns EOFError into
click.Abort, so the command printed nothing but "Aborted!", even with
-v. The extraction now catches the read errors an archive can raise,
names the file and the reason at critical level, says the file may be
truncated or not a gzip tarball, and exits 1. A plain .tar given to the
gzip reader gets the same message rather than a traceback.

tests/test_check_ios_sysdiagnose.py

@@ -1,4 +1,6 @@
 import logging
+import os
+import tarfile
 
 from click.testing import CliRunner
 
@@ -62,3 +64,29 @@ def test_check_sysdiagnose_warns_without_a_custom_module(tmp_path, caplog):
 
     assert result.exit_code == 0
     assert "No forensic sysdiagnose modules have been loaded" in caplog.text
+
+
+def _create_truncated_sysdiagnose_archive(tmp_path):
+    folder = tmp_path / "sysdiagnose_2026.01.01_00-00-00+0000_iPhone-OS_iPhone_23A000"
+    folder.mkdir()
+    (folder / "sysdiagnose.log").write_bytes(os.urandom(200_000))
+    archive = tmp_path / "sysdiagnose.tar.gz"
+    with tarfile.open(archive, "w:gz") as tar:
+        tar.add(folder, arcname=folder.name)
+    data = archive.read_bytes()
+    archive.write_bytes(data[: len(data) // 2])
+    return archive
+
+
+def test_check_sysdiagnose_reports_a_truncated_archive(tmp_path, caplog):
+    # A download that stopped halfway ends in EOFError from gzip, which Click
+    # would otherwise turn into a bare "Aborted!" with no reason given.
+    archive = _create_truncated_sysdiagnose_archive(tmp_path)
+
+    with caplog.at_level(logging.CRITICAL, logger="mvt"):
+        result = CliRunner().invoke(check_sysdiagnose, [str(archive)])
+
+    assert result.exit_code == 1
+    assert "Unable to read the sysdiagnose archive" in caplog.text
+    assert "truncated" in caplog.text
+    assert "Aborted!" not in result.output