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

install_postfixadmin.sh

@@ -2319,12 +2319,17 @@ 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
-   usermod -a -G dovecot $HTTP_USER > $log_file 2>&1
-   if [[ $? -eq 0 ]] ; then
-      echo_ok
+   if ! $(grep dovecot /etc/group > /dev/null) ; then
+      echo_skipped
+      warn "Group 'dovecot' not present.!"
    else
-      echo_failed
-      error "$(cat $log_file)"
+      usermod -a -G dovecot $HTTP_USER > $log_file 2>&1
+      if [[ $? -eq 0 ]] ; then
+         echo_ok
+      else
+         echo_failed
+         error "$(cat $log_file)"
+      fi
    fi
 fi