Add logic for checking empty files

Fix constructor

PDWEB-82

Author: Egor Martsynkovsky

commons/src/main/java/com/itextpdf/commons/utils/FileUtil.java

@@ -110,6 +110,21 @@ public static boolean fileExists(String path) {
         return false;
     }
 
+    /**
+     * Checks whether is provided file not empty.
+     *
+     * @param path the path to the file to be checked on emptiness
+     *
+     * @return {@code true} if such file is not empty, {@code false} otherwise
+     */
+    public static boolean isFileNotEmpty(String path) {
+        if (path != null) {
+            File f = new File(path);
+            return f.exists() && f.isFile() && f.length() > 0;
+        }
+        return false;
+    }
+
     /**
      * Checks whether there is a directory at the provided path.
      *

commons/src/main/java/com/itextpdf/commons/utils/ZipFileWriter.java

@@ -51,7 +51,7 @@ public ZipFileWriter(String archivePath) throws IOException {
         if (archivePath == null) {
             throw new IOException(CommonsExceptionMessageConstant.FILE_NAME_CAN_NOT_BE_NULL);
         }
-        if (FileUtil.fileExists(archivePath) || FileUtil.directoryExists(archivePath)) {
+        if (FileUtil.isFileNotEmpty(archivePath) || FileUtil.directoryExists(archivePath)) {
             throw new IOException(
                     MessageFormatUtil.format(CommonsExceptionMessageConstant.FILE_NAME_ALREADY_EXIST, archivePath));
         }