minor #14192 Update dom_crawler.rst (ThomasLandauer)

This PR was submitted for the 3.4 branch but it was merged into the 4.4 branch instead.

Discussion
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Update dom_crawler.rst

Since the expected `empty()` doesn't work, I explained how to check if a filter did find anything.

Commits
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5a70fcd Update dom_crawler.rst

Author: javiereguiluz

components/dom_crawler.rst

@@ -114,7 +114,8 @@ To remove a node the anonymous function must return false.
 .. note::
 
     All filter methods return a new :class:`Symfony\\Component\\DomCrawler\\Crawler`
-    instance with filtered content.
+    instance with the filtered content. To check if the filter actually
+    found something, use ``$crawler->count() > 0`` on this new crawler.
 
 Both the :method:`Symfony\\Component\\DomCrawler\\Crawler::filterXPath` and
 :method:`Symfony\\Component\\DomCrawler\\Crawler::filter` methods work with