added check for wrestic binary

debian/debian-essentials.sh

@@ -220,8 +220,11 @@ if [ $isInFile -eq 0 ]
         echo "Unattended upgrades already configured."
 fi
 
-# install or update wrestic
-curl -sL $(curl -s https://api.github.com/repos/alvaro17f/wrestic/releases/latest | grep browser_download_url | cut -d '"' -f 4) | sudo tar zxf - -C /usr/local/bin --overwrite
+# update wrestic
+if [[ -f /usr/local/bin/wrestic ]]
+    then
+        curl -sL $(curl -s https://api.github.com/repos/alvaro17f/wrestic/releases/latest | grep browser_download_url | cut -d '"' -f 4) | sudo tar zxf - -C /usr/local/bin --overwrite
+fi
 
 # install cronicle worker
 if [[ -f /opt/cronicle/conf/config.json ]]