Fix "No passwd entry for user '-'"

mxservicectl

@@ -19,6 +19,8 @@ function mxsrv_start_one() {
 
    . ${cfg}
 
+   test "$MX_SRV_USER" = "-" && MX_SRV_USER="root"
+
    case "${MX_SRV_SCRIPT}" in
        *.service)
            systemctl start "${MX_SRV_SCRIPT}" || true
@@ -41,6 +43,8 @@ function mxsrv_stop_one() {
 
    . ${cfg}
 
+   test "$MX_SRV_USER" = "-" && MX_SRV_USER="root"
+
    case "${MX_SRV_SCRIPT}" in
        *.service)
            systemctl stop "${MX_SRV_SCRIPT}" || true