fix(core): ensure initial value of QueryList length (#21980) (#21982)

Set initial value of `length` to `0`.

Fixes regression introduced by e544742156 (diff-a85dbe0991a7577ea24b49374e9ae90b) where the `length` property ceased to have initial value.

Closes #21980

PR Close #21982

packages/core/src/linker/query_list.ts

@@ -41,7 +41,7 @@ export class QueryList<T>/* implements Iterable<T> */ {
   private _results: Array<T> = [];
   public readonly changes: Observable<any> = new EventEmitter();
 
-  readonly length: number;
+  readonly length: number = 0;
   readonly first: T;
   readonly last: T;