Fix potential NPE when dumping child nodes

* This brings the childNafCheck method in line with the version in
  androidx.test.uiautomator.

Bug: 315023780
Test: manual
Change-Id: Ie5ba2340bedabc31f346c6e717353c7a5db0e90e

cmds/uiautomator/library/core-src/com/android/uiautomator/core/AccessibilityNodeInfoDumper.java

@@ -292,13 +292,17 @@ public class AccessibilityNodeInfoDumper {
         int childCount = node.getChildCount();
         for (int x = 0; x < childCount; x++) {
             AccessibilityNodeInfo childNode = node.getChild(x);
-
+            if (childNode == null) {
+                continue;
+            }
             if (!safeCharSeqToString(childNode.getContentDescription()).isEmpty()
-                    || !safeCharSeqToString(childNode.getText()).isEmpty())
+                    || !safeCharSeqToString(childNode.getText()).isEmpty()) {
                 return true;
+            }
 
-            if (childNafCheck(childNode))
+            if (childNafCheck(childNode)) {
                 return true;
+            }
         }
         return false;
     }