bug#36520: Form submition in eww doesn't work if file field is left empty

[Ivaylo Ilionov]

When submitting form with various fields including one optional

field for file upload, if the file filed is left empty - the

submition doesn't work.

The error is: Wrong type argument: stringp, nil

I've tracked the problem to the function 'eww-submit' which tries

to open a file for upload (the file was never initialized by the

html form).

My fix is to check if the property is set in the file "eww.el.gz" after

line 1435:

> ((equal (plist-get input :type) "file")

>  ;; FIX check if property :filename is not nil

>  (when (not (null (plist-get input :filename)))

>    (push (cons "file"

>         (list (cons "filedata"

>       (with-temp-buffer

>         (insert-file-contents

>          (plist-get input :filename))

>         (buffer-string)))

>        (cons "name" (plist-get input :name))

>        (cons "filename" (plist-get input :filename))))

>   values)))

Details about my emacs:

In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 2.24.32)

 of 2019-07-05 built on debian

Repository revision: f24d47359d9b6621215f20795d585c5024d91783

Repository branch: master

Windowing system distributor 'The X.Org Foundation', version 11.0.12004000

System Description: Debian GNU/Linux 10 (buster)