fix: remove redundant null check for SpotBugs compliance

Author: Shewale41

src/main/java/com/thealgorithms/datastructures/trees/ThreadedBinaryTree.java

@@ -59,7 +59,8 @@ public void insert(int value) {
 
         Node current = root;
         Node parent = null;
-        while (current != null) {
+
+        while (true) {
             parent = current;
             if (value < current.value) {
                 if (!current.leftIsThread && current.left != null) {