Fixed potentially odd NPE due to dangling elements in queue (#4123)

Author: shai-almog

maven/core-unittests/src/test/java/com/codename1/io/NetworkManagerTest.java

@@ -32,7 +32,8 @@ void setUp() throws Exception {
     }
 
     @AfterEach
-    void tearDown() {
+    void tearDown() throws Exception {
+        resetManagerState();
         Util.setImplementation(null);
         Storage.setStorageInstance(null);
     }