Avoid repeatedly altering desktop file

src/freedombone-image-customise

@@ -935,7 +935,9 @@ else
             rm /home/$MY_USERNAME/Desktop/tox.desktop
         fi
         if [ -f /home/$MY_USERNAME/Desktop/social.desktop ]; then
-            sed -i 's|Name=.*|Name=Social (Offline)|g' /home/$MY_USERNAME/Desktop/social.desktop
+            if ! grep -q "Offline" /home/$MY_USERNAME/Desktop/social.desktop; then
+                sed -i 's|Name=.*|Name=Social (Offline)|g' /home/$MY_USERNAME/Desktop/social.desktop
+            fi
         fi
         pkill qtox
     fi