Use ContainerNode::hasChildren() instead of firstChild() in conditionals

Source/core/editing/SpellChecker.cpp

Index: Source/core/editing/SpellChecker.cpp
diff --git a/Source/core/editing/SpellChecker.cpp b/Source/core/editing/SpellChecker.cpp
index c85a648c398a747f53d0a148c0d727b16c97aaa2..fb57b8b84a4eb81d8e87258c962b7c053072a98d 100644
--- a/Source/core/editing/SpellChecker.cpp
+++ b/Source/core/editing/SpellChecker.cpp
@@ -861,7 +861,7 @@ static Node* findFirstMarkable(Node* node)
             return node;
         if (node->renderer()->isTextControl())
             node = toRenderTextControl(node->renderer())->textFormControlElement()->visiblePositionForIndex(1).deepEquivalent().deprecatedNode();
-        else if (node->firstChild())
+        else if (node->hasChildren())
             node = node->firstChild();
         else
             node = node->nextSibling();