title: RNFetchBlob still creates empty file when none exists to download
body: <p>I am using the react-native-fetch-blob library. However, when a 404 message is sent it creates an empty file and calls it blag6.zip. This is my code:</p>
  
  <pre><code>try {
      response = await RNFetchBlob
      .config({
          path: RNFetchBlob.fs.dirs.DocumentDir + "/temp/blag6.zip"
      })
      .fetch(
          'POST',
          'http://example.com/data/getTestSet.php',
          {
              'Accept': 'application/json',
              'Content-Type': 'application/json'
          },
          JSON.stringify({
              'passcode': "pass123",
              'group_id': "1",
              'file': "ShgRG/suvA/blag.zip"
          })
      )
  
  
      temp_file = RNFS.DocumentDirectoryPath + "/temp/blag6.zip"
      output_path = RNFS.DocumentDirectoryPath + "/output
  
      await ZipArchive.unzip(temp_file, output_path)
      console.log("This line is never reached.")
  }
  catch (err){
      console.log(err)
  }
  </code></pre>
  
  <p>I get the following error:</p>
  
  <p><code>Error: Failed to extract file File too short to be a zip file: 0</code></p>
  
  <p>Is there a way to prevent RNFetchBlob from saving empty files and throw an error instead? How can I tell what the error is?</p>
  
  <p><strong>Update:</strong></p>
  
  <p>For now I am using a temporary fix with the following:</p>
  
  <pre><code>status = response.info().status
  
  //check if file exists here, throw error otherwise
  
  file_name = RNFetchBlob.fs.dirs.DocumentDir + "/temp/blag6.zip"
  
  file_stat = await RNFS.stat(file_name);
  file_size = file_stat.size;
  
  if (status != 200 || file_size == 0){
      await RNFS.unlink(file_name);
      throw "My error message";
  }
  </code></pre>
  
  <p>Is there a reason that RNFetchBlob still creates a file if none was available? Is there any way to prevent it from creating an empty file if there is no file to save?</p>