Add additional check to _getProgressFromStdErr
Add additional check to _getProgressFromStdErr

On v1.2.0, the onProgress event will occasionally fail with the following error:

/node_modules/fluent-ffmpeg/lib/processor.js:369
    var progress = ll.split(/frame=([0-9\s]+)fps=([0-9\s]+)q=([0-9\.\s]+)(L?)s
                      ^
TypeError: Cannot call method 'split' of undefined
    at FfmpegCommand.module.exports._getProgressFromStdErr (/home/ec2-user/EncoderInstance/node_modules/fluent-ffmpeg/lib/processor.js:369:23)
    at Socket.module.exports.saveToFile (/home/ec2-user/EncoderInstance/node_modules/fluent-ffmpeg/lib/processor.js:102:16)
    at Socket.EventEmitter.emit (events.js:88:17)
    at Pipe.onread (net.js:390:31)

This change adds a check for the 'll' variable before calling 'split'.
jleal52/node-fluent-ffmpeg,njoyard/node-fluent-ffmpeg,topaxi/node-fluent-ffmpeg,rhodgkins/node-fluent-ffmpeg,dchusovitin/node-fluent-ffmpeg,mcanthony/node-fluent-ffmpeg,timdp/node-fluent-ffmpeg,chazmo03/node-fluent-ffmpeg,snowkeeper/node-fluent-ffmpeg,streamablevideo/node-fluent-ffmpeg,mcanthony/node-fluent-ffmpeg,fluent-ffmpeg/node-fluent-ffmpeg,timdp/node-fluent-ffmpeg,whmountains/node-fluent-ffmpeg,fluent-ffmpeg/node-fluent-ffmpeg,rhodgkins/node-fluent-ffmpeg,streamablevideo/node-fluent-ffmpeg,fluent-ffmpeg/node-fluent-ffmpeg,whmountains/node-fluent-ffmpeg,jleal52/node-fluent-ffmpeg,njoyard/node-fluent-ffmpeg,dchusovitin/node-fluent-ffmpeg,chazmo03/node-fluent-ffmpeg,snowkeeper/node-fluent-ffmpeg,topaxi/node-fluent-ffmpeg,streamablevideo/node-fluent-ffmpeg,fritx/node-fluent-ffmpeg,fritx/node-fluent-ffmpeg