debian: Do not fail the bug-script if readlink fails

When readlink fails inside a $() the whole script fails. Remove the
«set -e» from the bug-script, as making it fail will cause programs
like reportbug to make it way harder to report bugs, which is
counterproductive.

Closes: #968397

debian/bug-script

 #!/bin/sh
 
-set -e
-
 for d in /bin /sbin /lib /lib32 /libo32 /libx32 /lib64; do
   linkname="$(readlink $d)"
   if [ "$linkname" = "usr$d" ] || [ "$linkname" = "/usr$d" ]; then