Resolve match_wildcard_for_single_variants pedantic clippy lint

    warning: wildcard matches only a single variant and will also match any future added variants
      --> gen/src/error.rs:43:13
       |
    43 |             _ => None,
       |             ^ help: try this: `Error::NoBridgeMod`
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#match_wildcard_for_single_variants
       = note: `-W clippy::match-wildcard-for-single-variants` implied by `-W clippy::pedantic`

gen/build/src/lib.rs

@@ -59,7 +59,6 @@
     clippy::match_bool,
     clippy::match_on_vec_items,
     clippy::match_same_arms,
-    clippy::match_wildcard_for_single_variants,
     clippy::module_name_repetitions,
     clippy::needless_doctest_main,
     clippy::needless_pass_by_value,

gen/cmd/src/main.rs

@@ -12,7 +12,6 @@
     clippy::match_bool,
     clippy::match_on_vec_items,
     clippy::match_same_arms,
-    clippy::match_wildcard_for_single_variants,
     clippy::module_name_repetitions,
     clippy::needless_pass_by_value,
     clippy::new_without_default,

gen/lib/src/lib.rs

@@ -21,7 +21,6 @@
     clippy::match_bool,
     clippy::match_on_vec_items,
     clippy::match_same_arms,
-    clippy::match_wildcard_for_single_variants,
     clippy::missing_errors_doc,
     clippy::module_name_repetitions,
     clippy::must_use_candidate,

gen/src/error.rs

@@ -40,7 +40,7 @@ impl StdError for Error {
             Error::Fs(err) => err.source(),
             Error::Utf8(_, err) => Some(err),
             Error::Syn(err) => err.source(),
-            _ => None,
+            Error::NoBridgeMod => None,
         }
     }
 }