Fix NVIDIA passthrough logic in container build

Refactored the NVIDIA GPU passthrough configuration to ensure device entries and related settings are only added when /dev/nvidia* devices are present. This prevents passthrough configuration attempts when no NVIDIA devices are detected, improving reliability and error messaging.

misc/build.func

@@ -2198,6 +2198,7 @@ build_container() {
         msg_info "Fix NVIDIA drivers on host, then recreate container or passthrough manually."
         return 0
       fi
+
       for d in /dev/nvidia* /dev/nvidiactl /dev/nvidia-modeset; do
         [[ -e "$d" ]] && NVIDIA_DEVICES+=("$d")
       done
@@ -2205,7 +2206,7 @@ build_container() {
       if [[ ${#NVIDIA_DEVICES[@]} -eq 0 ]]; then
         msg_warn "NVIDIA GPU detected but no /dev/nvidia* devices found"
         msg_warn "Please install NVIDIA drivers on host: apt install nvidia-driver"
-      fi
+      else
         if [[ "$CT_TYPE" == "0" ]]; then
           cat <<EOF >>"$LXC_CONFIG"
     # NVIDIA GPU Passthrough (privileged)
@@ -2216,7 +2217,7 @@ build_container() {
     lxc.mount.entry: /dev/nvidia-uvm dev/nvidia-uvm none bind,optional,create=file
     lxc.mount.entry: /dev/nvidia-uvm-tools dev/nvidia-uvm-tools none bind,optional,create=file
 EOF
-      fi
+
           if [[ -e /dev/dri/renderD128 ]]; then
             echo "lxc.mount.entry: /dev/dri/renderD128 dev/dri/renderD128 none bind,optional,create=file" >>"$LXC_CONFIG"
           fi
@@ -2229,7 +2230,7 @@ build_container() {
           return 0
         fi
       fi
-      }
+    fi
 
       # Debug output
       msg_debug "Intel devices: ${INTEL_DEVICES[*]}"