Plugin adds .plain to text extension when pass base64

[moeatsy]

 const reader = new FileReader();

  reader.onloadend = () => {
    console.log(blob.type) // 'text/plain'
    plugins.socialsharing.share(null, name, reader.result, null);
  };
  reader.readAsDataURL(blob);

When I trying to share text file at andoid, it adds .plain extension so new file name is file.txt.plain

[moeatsy]

have equal issue with xls files, its add .csv.vnd.ms-excel

[moeatsy]

fixed, library parsing filename from base64 string in different order rather than reader output

 const reader = new FileReader();
  const { type } = blob;

  reader.onloadend = () => {
    const base64Data = reader.result.substr(reader.result.indexOf('base64,') + 7);

    plugins.socialsharing.shareWithOptions({
      files: [`df:${name};data:${type};base64,${base64Data}`],
    });
  };

  reader.readAsDataURL(blob);

thanks to issue #918