Print error message on empty BPF

This is useful when we're not sure if a filter is installed or not

Author: qua3k

lib/seccomp-tools/dumper.rb

@@ -182,6 +182,7 @@ def dump_by_pid(pid, limit, &block)
           begin
             bpf = Ptrace.seccomp_get_filter(pid, i)
           rescue Errno::ENOENT, Errno::EINVAL
+            Logger.error('No seccomp filters installed')
             break
           end
           collect << (block.nil? ? bpf : yield(bpf, nil))