array: Fix removal of elements in the second half of an array

Memory beyond the end of the array was moved when array elements in the
second half of an array were removed.

Fixes #548.

src/libstrongswan/collections/array.c

@@ -141,7 +141,7 @@ static void remove_tail(array_t *array, int idx)
 	/* move all items after idx one down */
 	memmove(array->data + get_size(array, idx + array->head),
 			array->data + get_size(array, idx + array->head + 1),
-			get_size(array, array->count - idx));
+			get_size(array, array->count - 1 - idx));
 	array->count--;
 	array->tail++;
 }