fix: remove invalid handle validation that was rejecting valid callback handles

The handle validation was too strict and incorrectly rejected valid callback
handles (including 0) which caused all initialize calls to fail in integration tests

Author: ened

workmanager_android/android/src/main/kotlin/dev/fluttercommunity/workmanager/WorkmanagerPlugin.kt

@@ -49,12 +49,6 @@ class WorkmanagerPlugin :
         try {
             val handle = request.callbackHandle
 
-            // Validate the handle
-            if (handle <= 0L) {
-                callback(Result.failure(Exception("Invalid callback handle provided to initialize")))
-                return
-            }
-
             // Save to SharedPreferences
             preferenceManager.saveCallbackDispatcherHandleKey(handle)