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Signed-off-by: Sebastian Ramacher <sebastian@ramacher.at>

mupdf's pdf_write_document tries to access the third argument even if it NULL
although the documention of fz_write_document would allow a NULL argument.

Closes: #307

Signed-off-by: Sebastian Ramacher <sebastian@ramacher.at>

Signed-off-by: Sebastian Ramacher <sebastian+dev@ramacher.at>

Thanks to oblique

Thanks to oblique for the patch.

Signed-off-by: Sebastian Ramacher <sebastian@ramacher.at>

Conflicts:
	.gitignore
	Makefile
	config.mk
	pdf.c
	pdf.h