Add check for return code of retried command

[mimi1vx]

This fixes poo#138491

When command failed with retries eq "0" retry script always return 0 as success which can be false positive

So this change adds check for return code if $retries -eq 0

[okurz]

just one minor typo in the string, rest looks great!

[perlpunk]

This still returns 1 if there were more than zero retries:

% ./retry -r 3 -s 1 -- perl -wE'print "input: ";chomp(my $rc=<STDIN>); exit $rc'
input: 1
Retrying up to 3 more times after sleeping 1s …
input: 1
Retrying up to 2 more times after sleeping 1s …
input: 1
Retrying up to 1 more times after sleeping 1s …
input: 0
% echo $?
1