rustdoc: add fast path for empty generic args

Author: fmease

src/librustdoc/clean/utils.rs

@@ -81,6 +81,11 @@ pub(crate) fn ty_args_to_args<'tcx>(
     has_self: bool,
     owner: DefId,
 ) -> Vec<GenericArg> {
+    // Fast path which avoids executing the query `generics_of`.
+    if ty_args.skip_binder().is_empty() {
+        return Vec::new();
+    }
+
     let params = &cx.tcx.generics_of(owner).params;
     let mut elision_has_failed_once_before = false;