title: Using RNFetchBlob.fs.cp with uri got from react-native-document-picker causeing error
body: <p>react-native: 0.59.9,
  react-native-document-picker: 3.2.4,
  rn-fetch-blob: 0.10.15,</p>
  
  <p>In the App, I use 'react-native-document-picker' to select files on the phone, and get the uris of the files, then call 'RNFetchBlob.fs.cp(uri, destPath)' to copy the file to the specific folder.
  However, the copy file method may fail depends on the uri returned from 'react-native-document-picker'.</p>
  
  <p>For example, while selecting the file in different directory,
  if the uri returned as "content://com.android.externalstorage.documents/document/primary%3ADownload%2FCopyFile.pdf",
  it works, 
  but if the uri returned as "content://com.android.providers.downloads.documents/document/17",
  then RNFetchBlob.fs.cp will cause a error of 'Attempt to invoke virtual method 'boolean java.lang.String.startsWith(java.lang.String)' on a null object reference'</p>
  
  <p>I guess it fails because of the uri format with 'com.android.providers.downloads', is there any react-native library deal with the uri so that RNFetchBlob.fs can work on it?</p>