new_arena(): In error cases, reset the number of available pools to 0.

Else the pymalloc malloc will go insane the next time it's called.

Objects/obmalloc.c

@@ -424,6 +424,7 @@ new_arena(void)
 
 error:
 	PyMem_FREE(bp);
+	nfreepools = 0;
 	return NULL;
 }