Nesting index multiplication assignment fixed

This affects all arithmetic types applied to inner-nested compounds.

test/scripts/index-arrays.toy

@@ -71,6 +71,14 @@
 	assert a[0][0] == [42], "nested indexing failed";
 }
 
+//test nested indexing multipliciation assignment
+{
+	var a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
+
+	a[1][1] *= 10;
+
+	assert a == [[1, 2, 3], [4, 50, 6], [7, 8, 9]], "nested indexing multipliciation assignment failed";
+}
 
 //test combine example
 {