refactor(diff): set oldProps default value on declaration (#4959)

Author: ali-garajian

src/diff/index.js

@@ -415,7 +415,7 @@ function diffElementNodes(
 	isHydrating,
 	refQueue
 ) {
-	let oldProps = oldVNode.props;
+	let oldProps = oldVNode.props || EMPTY_OBJ;
 	let newProps = newVNode.props;
 	let nodeType = /** @type {string} */ (newVNode.type);
 	/** @type {any} */
@@ -485,8 +485,6 @@ function diffElementNodes(
 		// If excessDomChildren was not null, repopulate it with the current element's children:
 		excessDomChildren = excessDomChildren && slice.call(dom.childNodes);
 
-		oldProps = oldVNode.props || EMPTY_OBJ;
-
 		// If we are in a situation where we are not hydrating but are using
 		// existing DOM (e.g. replaceNode) we should read the existing DOM
 		// attributes to diff them