fixes attestation parsing in witness-verify

Addresses an issue where the attestation parsing in
`witness-verify` would fail when the attestation file
was empty or contained invalid JSON. Now, it handles
empty files gracefully and catches parsing errors.

Author: kriscoleman

Makefile

@@ -114,7 +114,7 @@ witness-verify:
 	echo ""; \
 	if [ -f conda-build.attestation.json ] && [ -s conda-build.attestation.json ]; then \
 		echo "Attestation summary:"; \
-		python -c "import json, sys; try: data = json.load(sys.stdin); print(f'  Type: {data.get(\"type\", \"unknown\")}') except: print('  Type: unable to parse attestation')" < conda-build.attestation.json; \
+		python -c "import json, sys; content = sys.stdin.read(); data = json.loads(content) if content else {}; print(f\"  Type: {data.get('type', 'unknown')}\")" < conda-build.attestation.json 2>/dev/null || echo "  Type: unable to parse attestation"; \
 	elif [ -f conda-build.attestation.json ]; then \
 		echo "Warning: Attestation file exists but is empty"; \
 	else \