checker: handle void in struct field init (fix #13944) (#14876)

vlib/v/checker/struct.v

@@ -377,6 +377,9 @@ pub fn (mut c Checker) struct_init(mut node ast.StructInit) ast.Type {
 				expected_type = field_info.typ
 				c.expected_type = expected_type
 				expr_type = c.expr(field.expr)
+				if expr_type == ast.void_type {
+					c.error('`$field.expr` (no value) used as value', field.pos)
+				}
 				if !field_info.typ.has_flag(.optional) {
 					expr_type = c.check_expr_opt_call(field.expr, expr_type)
 				}