*.c: Be more careful about `PySequence_Size'.

This can be implemented by Python, so it can throw exceptions.
Fortunately, Python checks that the result is nonnegative, so we don't
have to worry about that.

diff --git a/catacomb.c b/catacomb.c
index daa404a..e24e5ec 100644 (file)
--- a/catacomb.c
+++ b/catacomb.c
@@ -76,7 +76,8 @@ PyObject *mexp_common(PyObject *me, PyObject *arg,
     arg = PyTuple_GetItem(arg, 0);
   Py_INCREF(arg);
   if (!PySequence_Check(arg)) TYERR("not a sequence");
-  n = PySequence_Size(arg); if (!n) { z = id(me); goto end; }
+  n = PySequence_Size(arg); if (n < 0) goto end;
+  if (!n) { z = id(me); goto end; }
   x = PySequence_GetItem(arg, 0);
   if (PySequence_Check(x))
     flat = 0;