Fix NPE when invoking copyNecessaryFilesFromCurrentPackage() method on Android (microsoft#2566)

* Fix NPE when invoking `copyNecessaryFilesFromCurrentPackage()` method on Android.

* Add logging and check if the path exists

* fixup

---------

Co-authored-by: Anatoly Pristensky <v-anatpr@microsoft.com>

Author: robxyy

android/app/src/main/java/com/microsoft/codepush/react/CodePushUpdateUtils.java

@@ -98,7 +98,10 @@ private static String computeHash(InputStream dataStream) {
     }
 
     public static void copyNecessaryFilesFromCurrentPackage(String diffManifestFilePath, String currentPackageFolderPath, String newPackageFolderPath) throws IOException {
-        FileUtils.copyDirectoryContents(currentPackageFolderPath, newPackageFolderPath);
+        if (currentPackageFolderPath == null || !new File(currentPackageFolderPath).exists()) {
+            CodePushUtils.log("Unable to copy files from current package during diff update, because currentPackageFolderPath is invalid.");
+            return;
+        }
         JSONObject diffManifest = CodePushUtils.getJsonObjectFromFile(diffManifestFilePath);
         try {
             JSONArray deletedFiles = diffManifest.getJSONArray("deletedFiles");