$/="\n\0"; will fail if the file contains character U+0Axx followed by U+yy00 (for any values "xx" and "yy").

Also, you should replace characters outside iso-latin-1 with some fixed character (such as "?") rather than some random character.

This fixes both problems: 

local $/ = "\x0A\x00";
for (
    my $line = '';
    defined( $_ = <> );
    $line = ''
) {
    $line .= $_;
    redo if length($line) % 2 != 0;

    print
        pack 'C*',
        map { $_ <= 0xFF ? $_ : '?' }
        unpack 'v*',
        $line;

    #   -or-
    # print utf16le($line)->latin1();
}

[download]

(Assumes each file in @ARGV is properly formed, i.e. contain an even number of bytes.)

In reply to Re^2: Mysterious Whitespaces between each character in a file (hack for 5.6.x) by ikegami
in thread Mysterious Whitespaces between each character in a file by 1wax

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