…umpy#28898)When running the scipy 1.15 test suite testsignal/tests/test_signaltools.py::test_lfilter_bad_object, with Pythonbuilt in debug mode, we see the following error:```Fatal Python error: _Py_CheckSlotResult: Slot * of type float succeeded with an exception set````None` ends up as the first argument to `dot`, and this triggers anerror from PyFloat_Multiply. Once an error has occurred, we must avoidcalling multiply again, since it asserts that PyErr_Occurred() is falseif the output is a non-error, which will fail if an error was set atentry.