Use then_some in try_join

Author: smoelius

clippy_utils/src/ty/type_certainty/certainty.rs

@@ -41,13 +41,7 @@ impl Meet for Option<DefId> {
 impl TryJoin for Option<DefId> {
     fn try_join(self, other: Self) -> Option<Self> {
         match (self, other) {
-            (Some(lhs), Some(rhs)) => {
-                if lhs == rhs {
-                    Some(Some(lhs))
-                } else {
-                    None
-                }
-            },
+            (Some(lhs), Some(rhs)) => (lhs == rhs).then_some(Some(lhs)),
             (Some(def_id), _) | (_, Some(def_id)) => Some(Some(def_id)),
             (None, None) => Some(None),
         }