Use is_valid for Id

src/lang.rs

@@ -28,7 +28,6 @@ const FADE_PER_DAY: f32 = 0.95;
 #[derive(Clone, PartialEq, Eq, Debug, Hash, Copy)]
 pub(crate) struct Id(u32);
 pub const INVALID_ID: Id = Id(0);
-
 impl FromStr for Id {
     type Err = ParseIntError;
 
@@ -69,6 +68,12 @@ impl ToSql for Id {
     }
 }
 
+impl Id {
+    pub(crate) fn is_valid(self) -> bool {
+        self.0 != 0
+    }
+}
+
 #[derive(Clone, Debug)]
 pub struct KanaSet {
     name: String,
@@ -703,4 +708,4 @@ impl DeckSettings {
     pub fn require_speech(&self) -> bool {
         self.forward == "speech" || self.backward == "speech"
     }
-}
+}