add condition inside download event, before pass it to event callback.

[RZulfikri]

Related issue: #811

Problem
When I called multiple RNFS.downloadFile, begin and progress callbacks return all events that occur, not only event that related to that instance only.

For example, I have 2 download process with jobId 1 and 2. In begin callback I'll receive responses of jobId 1 and 2, also in the progress callback.

Solution
When I check the native code there is nothing wrong with that, so I add conditions in event listener to check jobId before pass it event callback.

    if (options.begin) {
      subscriptions.push(RNFS_NativeEventEmitter.addListener('DownloadBegin', (res) => {
        if (res.jobId === jobId) options.begin(res);
      }));
    }

    if (options.progress) {
      subscriptions.push(RNFS_NativeEventEmitter.addListener('DownloadProgress', (res) => {
        if (res.jobId === jobId) options.progress(res);
      }));
    }

    if (options.resumable) {
      subscriptions.push(RNFS_NativeEventEmitter.addListener('DownloadResumable', (res) => {
        if (res.jobId === joibId) options.resumable(res);
      }));
    }

[itinance]

Many thanks!