CAPI exception case in converting long to double.

src/runtime/float.cpp

@@ -928,6 +928,9 @@ template <ExceptionStyle S> static BoxedFloat* _floatNew(Box* a) noexcept(S == C
             else
                 throwCAPIException();
         }
+
+        // Make sure that we're not in an error state when we return a non-NULL value.
+        assert(!PyErr_Occurred());
         return new BoxedFloat(a_f);
     } else if (a->cls == str_cls || a->cls == unicode_cls) {
         BoxedFloat* res = (BoxedFloat*)PyFloat_FromString(a, NULL);