radicle/tor: Fixes

Fixes two earlier mistakes:
 1. In `fb18083`, `fn null_to_default` was added, which is only
    conditionally used if the feature "tor" is enabled, so also
    only conditionally compile the function.
 2. In `1e13268`, the `impl Arbitrary` for AddressType` was not
    properly adjusted for the case where the newly introduced
    feature "tor" is disabled.

crates/radicle/src/serde_ext.rs

@@ -47,6 +47,7 @@ where
 }
 
 /// Deserialize a value, but if it is `null`, return the default value.
+#[cfg(feature = "tor")]
 pub(crate) fn null_to_default<'de, D, T>(deserializer: D) -> Result<T, D::Error>
 where
     T: serde::Deserialize<'de> + Default,

crates/radicle/src/test/arbitrary.rs

@@ -208,7 +208,12 @@ impl Arbitrary for MockRepository {
 
 impl Arbitrary for AddressType {
     fn arbitrary(g: &mut qcheck::Gen) -> Self {
-        let t = *g.choose(&[1, 2, 3, 4]).unwrap() as u8;
+        #[cfg(not(feature = "tor"))]
+        let types = [1, 2, 3];
+        #[cfg(feature = "tor")]
+        let types = [1, 2, 3, 4];
+
+        let t = *g.choose(&types).unwrap() as u8;
 
         AddressType::try_from(t).unwrap()
     }