vfmt: fix formatting for an option array of anon structs (fix #23841) (#23844)

vlib/v/fmt/struct.v

@@ -169,6 +169,9 @@ fn (mut f Fmt) write_anon_struct_field_decl(field_typ ast.Type, field_anon_decl
 				elem_sym := f.table.sym(sym.info.elem_type)
 				if elem_sym.info is ast.Struct {
 					if elem_sym.info.is_anon {
+						if field_typ.has_flag(.option) {
+							f.write('?')
+						}
 						f.write('[]'.repeat(sym.info.nr_dims))
 						f.write_anon_struct_field_decl(sym.info.elem_type, field_anon_decl)
 						return true

vlib/v/fmt/tests/array_option_anon_struct_keep.vv

@@ -0,0 +1,22 @@
+module main
+
+import json
+
+struct Data {
+mut:
+	a_token ?[]string
+	dfv     ?[]struct {
+		key string
+	}
+}
+
+fn main() {
+	j := '{
+	"a_token2": ["one", "two"],
+	"a_email2": {
+		"email": "email@email.ru"
+		}
+	}'
+	d := json.decode(Data, j)!
+	println(d)
+}