decode: fix wrong indention for tables' comments (#892)

marshaler.go

@@ -983,12 +983,12 @@ func (enc *Encoder) encodeSliceAsArrayTable(b []byte, ctx encoderCtx, v reflect.
 	scratch = append(scratch, "]]\n"...)
 	ctx.skipTableHeader = true
 
+	b = enc.encodeComment(ctx.indent, ctx.options.comment, b)
+
 	if enc.indentTables {
 		ctx.indent++
 	}
 
-	b = enc.encodeComment(ctx.indent, ctx.options.comment, b)
-
 	for i := 0; i < v.Len(); i++ {
 		if i != 0 {
 			b = append(b, "\n"...)

marshaler_test.go

@@ -1208,7 +1208,7 @@ func TestMarhsalIssue888(t *testing.T) {
 	}
 
 	type Cfg struct {
-		Custom []Thing
+		Custom []Thing `comment:"custom config"`
 	}
 
 	buf := new(bytes.Buffer)
@@ -1223,7 +1223,8 @@ func TestMarhsalIssue888(t *testing.T) {
 	encoder := toml.NewEncoder(buf).SetIndentTables(true)
 	encoder.Encode(config)
 
-	expected := `[[Custom]]
+	expected := `# custom config
+[[Custom]]
   # my field A
   FieldA = 'field a 1'
   # my field B