inline pointer_to_struce mode: update comments. return error on point…

…er not to struct

bson/bson.go

@@ -748,8 +748,8 @@ func getStructInfo(st reflect.Type) (*structInfo, error) {
 				inlineMap = info.Num
 			case reflect.Ptr:
 				// allow only pointer to struct
-				if field.Type.Elem().Kind() != reflect.Struct {
-					break
+				if kind := field.Type.Elem().Kind(); kind != reflect.Struct {
+					return nil, errors.New("Option ,inline allows a pointer only to a struct, was given pointer to " + kind.String())
 				}
 
 				field.Type = field.Type.Elem()
@@ -773,7 +773,7 @@ func getStructInfo(st reflect.Type) (*structInfo, error) {
 					fieldsList = append(fieldsList, finfo)
 				}
 			default:
-				panic("Option ,inline needs a struct value or map field")
+				panic("Option ,inline needs a struct value or a pointer to a struct or map field")
 			}
 			continue
 		}

bson/encode.go

@@ -229,6 +229,12 @@ func (e *encoder) addStruct(v reflect.Value) {
 		if info.Inline == nil {
 			value = v.Field(info.Num)
 		} else {
+			// as pointers to struct are allowed here,
+			// there is no guarantee that pointer won't be nil.
+			//
+			// It is expected allowed behaviour
+			// so info.Inline MAY consist index to a nil pointer
+			// and that is why we safely call v.FieldByIndex and just continue on panic
 			field, errField := safeFieldByIndex(v, info.Inline)
 			if errField != nil {
 				continue