Don't error-out with a traceback if we encounter struct.unpack-related errors...

Don't error-out with a traceback if we encounter struct.unpack-related errors when parsing .pyc files. (Closes: Debian:#1064973)

We should actually make the parsing *work*, but at least this won't cause
diffoscope to quit in the meantime.

diffoscope/comparators/python.py

@@ -55,7 +55,7 @@ class PycFile(File):
                     source="Python bytecode",
                 )
             ]
-        except (ValueError, IndexError) as exc:
+        except (ValueError, IndexError, struct.error) as exc:
             self.add_comment("Could not decompile bytecode: {}".format(exc))
             return []