Restructure code to avoid assignment expression warning. (#2833)

* Restructure code to avoid assignment expression warning.

Author: eamonnmcmanus

gson/src/main/java/com/google/gson/internal/Excluder.java

@@ -147,7 +147,10 @@ private TypeAdapter<T> delegate() {
         // A race might lead to `delegate` being assigned by multiple threads but the last
         // assignment will stick
         TypeAdapter<T> d = delegate;
-        return d != null ? d : (delegate = gson.getDelegateAdapter(Excluder.this, type));
+        if (d == null) {
+          d = delegate = gson.getDelegateAdapter(Excluder.this, type);
+        }
+        return d;
       }
     };
   }