#15: use the C locale to portably parse the PDF header

On a machine where the locale is set to something not equivalent to
ASCII, the call to `awk' in `get_pdf_version()' will throw the following
error:

  awk: cmd. line:1: (FILENAME=- FNR=1) warning: Invalid multibyte data
  detected. There may be a mismatch between your data and your locale.

This can be fixed by forcing the C locale by prepending the call to awk
with `LC_ALL=C'.

Reported and fixed by Laurent MUGNIER.

Resolves #15.

shrinkpdf.sh

@@ -3,7 +3,7 @@
 # https://github.com/aklomp/shrinkpdf
 # Licensed under the 3-clause BSD license:
 #
-# Copyright (c) 2014-2022, Alfred Klomp
+# Copyright (c) 2014-2023, Alfred Klomp
 # All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
@@ -65,13 +65,12 @@ get_pdf_version ()
 {
 	# $1 is the input file. The PDF version is contained in the
 	# first 1024 bytes and will be extracted from the PDF file.
-	pdf_version=$(cut -b -1024 "$1" | awk 'BEGIN { found=0 }{ if (match($0, "%PDF-[0-9]\\.[0-9]") && ! found) { print substr($0, RSTART + 5, 3); found=1 } }')
+	pdf_version=$(cut -b -1024 "$1" | LC_ALL=C awk 'BEGIN { found=0 }{ if (match($0, "%PDF-[0-9]\\.[0-9]") && ! found) { print substr($0, RSTART + 5, 3); found=1 } }')
 	if [ -z "$pdf_version" ] || [ "${#pdf_version}" != "3" ]; then
 		return 1
 	fi
 }
 
-
 check_input_file ()
 {
 	# Check if the given file exists.