phpwkhtmltopdf: Failed without error message

Similar problem as #99 and #97 but I think that this is a bug.

My code is fine, and command is:

wkhtmltopdf --encoding 'UTF-8' --dpi '96' --no-outline '/tmp/tmp_wkhtmlto_pdf_GRP6cv.html' '/tmp_wkhtmlto_pdf_hw2PnV.pdf'

If I execute this script from terminal, this is the log:

The switch --no-outline, is not support using unpatched qt, and will be ignored.Loading page (1/2)
Printing pages (2/2)                                               
Done

But phpwkhtmltopdf response an error and does not generate the PDF.

"Failed without error message: wkhtmltopdf --encoding 'UTF-8' --dpi '96' --no-outline '/tmp/tmp_wkhtmlto_pdf_GRP6cv.html' '/tmp/tmp_wkhtmlto_pdf_hw2PnV.pdf'"

This file generated from terminal is a valid PDF file /tmp/tmp_wkhtmlto_pdf_hw2PnV.pdf

Maybe some error checking critical wkhtmltopdf errors?

Thanks.