Fix handling of non-existing inputs and other extractor errors

spec._extractor() raises ExtractorError if and when an error occurs and
not an InvalidSpec, so handle this exception in the except clause.

This ensures that we give the expected error instead of a full
backtrace when specifying a non-existing file, for example.

abi3audit/_cli.py

@@ -20,6 +20,7 @@
 from abi3audit._audit import AuditError, AuditResult, audit
 from abi3audit._extract import (
     Extractor,
+    ExtractorError,
     InvalidSpec,
     PyPISpec,
     SharedObjectSpec,
@@ -238,7 +239,7 @@ def main() -> None:
             status.update(f"auditing {spec}")
             try:
                 extractor = spec._extractor()
-            except InvalidSpec as e:
+            except ExtractorError as e:
                 console.log(f"[red]:thumbs_down: processing error: {e}")
                 sys.exit(1)