apt: fix check_hel_packages script

apt/files/check_held_packages.sh

@@ -2,10 +2,14 @@
 
 is_held() {
     package=$1
-
     apt-mark showhold ${package} | grep --silent ${package}
 }
 
+is_installed() {
+    package=$1
+    dpkg -l "${package}" 2>/dev/null | grep -q -E '^(i|h)i'
+}
+
 config_file="/etc/evolinux/apt_hold_packages.cf"
 return_code=0
 
@@ -15,7 +19,7 @@ if [ -f ${config_file} ]; then
     if [ -n "${packages}" ]; then
         for package in ${packages}; do
             if [ -n "${package}" ]; then
-                if ! is_held ${package}; then
+                if is_installed ${package} && ! is_held ${package}; then
                     apt-mark hold ${package}
                     >&2 echo "Package \`${package}' has been marked \`hold'."
                     return_code=1