Print warning instead of error if group 'dovecot' does not exist.

install_postfixadmin.sh

@@ -2318,6 +2318,10 @@ fi
 echononl "\tAdd Apache User (${HTTP_USER}) to group 'dovecot'.."
 if getent group dovecot 2> /dev/null | grep -q "\b${HTTP_USER}\b" > /dev/null 2>&1 ; then
    echo_skipped
+else
+   if ! $(grep dovecot /etc/group > /dev/null) ; then
+      echo_skipped
+      warn "Group 'dovecot' not present.!"
    else
       usermod -a -G dovecot $HTTP_USER > $log_file 2>&1
       if [[ $? -eq 0 ]] ; then
@@ -2327,6 +2331,7 @@ else
          error "$(cat $log_file)"
       fi
    fi
+fi
 
 
 # - After finished, you must alos change the value of $CONF['configured']