cgen: fix anon struct init passing (fix #24879) (#24884)

Author: felipensp

vlib/v/gen/c/cgen.v

@@ -3118,7 +3118,7 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type_raw ast.Type, expected_typ
 	}
 	if (exp_sym.kind == .function && !expected_type.has_option_or_result())
 		|| (g.inside_struct_init && expected_type == ast.voidptr_type
-		&& expected_type != got_type_raw) {
+		&& expected_type != got_type_raw && expr !is ast.StructInit) {
 		g.write('(voidptr)')
 	}
 	// no cast

vlib/v/tests/structs/struct_init_passing_test.v

@@ -0,0 +1,22 @@
+module main
+
+import json
+
+struct Definition {
+	version u8
+}
+
+struct Logic {
+	run fn () i8 @[required]
+}
+
+fn test_main() {
+	logic := Logic{
+		run: fn () i8 {
+			json.encode_pretty(Definition{})
+			return 0
+		}
+	}
+	logic.run()
+	assert true
+}