fix: IncomingForm end event emitted twice

[jimmyolo]

closes to #810

[GrosSacASac]

Thanks

[gaganjot99]

Issue still persisting for me.
I just reinstalled formidable, end event again is being emitted twice
I have files input, For some reason it only happens when I include only one file but for two or more files it works perfectly.

[tunnckoCore]

use npm install node-formidable/formidable (the master branch), it's not yet in NPM i think.

@gaganjot99

[gaganjot99]

Thanks