array: Number of items in get_size() is unsigned

Otherwise, array->esize is promoted to int and if array->esize * num
results in a value > 0x7fffffff the return value would be incorrect due
the implicit sign extension when getting cast to size_t.

src/libstrongswan/collections/array.c

@@ -49,7 +49,7 @@ struct array_t {
 /**
  * Get the actual size of a number of elements
  */
-static size_t get_size(array_t *array, int num)
+static size_t get_size(array_t *array, u_int32_t num)
 {
 	if (array->esize)
 	{