More bug #1077106 stuff, sorry -- modem induced impatiece!

This should go on whatever bugfix branches the other fetches up on.
diff --git a/Objects/stringobject.c b/Objects/stringobject.c
index b8e5f41..b90221a 100644
--- a/Objects/stringobject.c
+++ b/Objects/stringobject.c
@@ -52,6 +52,7 @@
 PyString_FromStringAndSize(const char *str, int size)
 {
 	register PyStringObject *op;
+	assert(size >= 0);
 	if (size == 0 && (op = nullstring) != NULL) {
 #ifdef COUNT_ALLOCS
 		null_strings++;