file-access errors on ghostscript >= 9.50

@stuart-little is already working on this.

Since Jun 24, 2021.

For newer `gs` versions *every* run of `pdf2archive` results in this error being thrown right at the top of the output:

```
GPL Ghostscript 9.54.0: Unrecoverable error, exit code 1
```
After some investigation, I tracked it down to a file-access error related to the "safe" mode [that is the default](https://ghostscript.com/doc/9.50/Use.htm#Safer) in `gs` versions `9.50` and higher.

The following patch fixes it (it's literally a one-line change). I'd be happy to make that into a PR if you think it useful.

Patch:
```
Date: Sat Jun 12 13:47:26 2021 -0400

add '-dNOSAFER' option to eliminate gs file-access error

diff --git a/pdf2archive b/pdf2archive
index bac84be..e808079 100755
--- a/pdf2archive
+++ b/pdf2archive
@@ -249,7 +249,7 @@ quit
# use 'LC_CTYPE=C && LANG=C && echo "$METADUMP" ...' in the
# variable assignments; however, this produces bad PDF files.
#
-METADUMP=$(gs -dNODISPLAY -q -sFile="$INPUT" $INFOTMPFILE | iconv -f utf-8 -t utf-8 -c)
+METADUMP=$(gs -dNOSAFER -dNODISPLAY -q -sFile="$INPUT" $INFOTMPFILE | iconv -f utf-8 -t utf-8 -c)
[ -z ${PDFTITLE+x} ] && PDFTITLE=$(echo "$METADUMP" | grep "__knowninfoTitle: " | sed "s/^__knowninfoTitle: //g")
[ -z ${PDFAUTHOR+x} ] && PDFAUTHOR=$(echo "$METADUMP" | grep "__knowninfoAuthor: " | sed "s/^__knowninfoAuthor: //g")
[ -z ${PDFSUBJECT+x} ] && PDFSUBJECT=$(echo "$METADUMP" | grep "__knowninfoSubject: " | sed "s/^__knowninfoSubject: //g")
```