try to fix the update function.

linux-game-manager.sh

@@ -47,7 +47,12 @@ export DIALOGOPTS='--no-lines --visit-items'
 
 # Check for updates
 check_update() {
-    local branch="$(git rev-parse --abbrev-ref HEAD)"
+    local url="$(git ls-remote --get-url)"
+    if [[ "$url" =~ ^ssh://|git@ ]] || [[ -z "$url" ]]; then
+        return
+    fi
+    git fetch
+    local branch="$(git rev-parse --abbrev-ref HEAD 2> /dev/null)"
     local localSha="$(git rev-parse origin/${branch})"
     local remoteSha="$(git rev-parse refs/remotes/origin/${branch})"
     if [[ "${localSha}" == "${remoteSha}" ]]; then