vdoc: fix segfault on `v doc -m -f html vlib`

cmd/tools/vtest-parser.v

@@ -97,7 +97,7 @@ fn main() {
 
 fn process_cli_args() &Context {
 	mut context := &Context{
-		pref: 0
+		pref: pref.new_preferences()
 	}
 	context.myself = os.executable()
 	mut fp := flag.new_flag_parser(os.args_after('test-parser'))

vlib/v/doc/doc.v

@@ -113,7 +113,7 @@ pub fn new(input_path string) Doc {
 		time_generated: time.now()
 	}
 	d.fmt = fmt.Fmt{
-		pref: 0
+		pref: d.prefs
 		indent: 0
 		is_debug: false
 		table: d.table

vlib/v/pref/default.v

@@ -10,8 +10,8 @@ pub const (
 	default_module_path = os.vmodules_dir()
 )
 
-pub fn new_preferences() Preferences {
-	mut p := Preferences{}
+pub fn new_preferences() &Preferences {
+	mut p := &Preferences{}
 	p.fill_with_defaults()
 	return p
 }