more checks in scripts

debian/preinst

@@ -1,4 +1,6 @@
 #!/bin/sh
 if [ -e /usr/lib/xrdp/xrdp ]; then
+  if [ -e /etc/init.d/xrdp_control.sh ]; then
     /etc/init.d/xrdp_control.sh stop
+  fi
 fi

debian/prerm

@@ -1,4 +1,6 @@
 #!/bin/sh
 if [ -e /usr/lib/xrdp ]; then
+  if [ -e /etc/init.d/xrdp_control.sh ]; then
     /etc/init.d/xrdp_control.sh stop
+  fi
 fi