Fix: Set exit code to the total number of conversion failures

Problem: Whether there were conversion failures or not, pacpl always
ends with exit code 0, which makes it not practical to use it from a
shell script, since it would be necessary to parse the final message to
discover whether there were failures.
Solution: As $total_failures has lexical file scope, after finishing
processing all files, we can call "exit $total_failures", so that any
scripts calling pacpl can know if it was 100%  successful or had some
failure just by testing the exit code.

pacpl.in

@@ -3595,7 +3595,7 @@ if (@ARGV) {
 
 load_user_modules() if $config{IMPORTM} == 1;
 
-if ($to and @ARGV and not $rip) { proc_input(); } 
+if ($to and @ARGV and not $rip) { proc_input(); exit $total_failed; } 
 
 elsif ($to and $rip) { proc_cd(); }
 elsif ($my_encoder and not $to) { show_encoders(); }