live: check permissions when trying to fetch file via unicast

check sufficient permissions and bail out in case of issues.

src/live/ogOperations.py

@@ -201,7 +201,11 @@ class OgLiveOperations:
                 not tip_check_csum(repo, name)):
                 self._copy_image_to_cache(name)
         else:
+            if os.access(f'/opt/opengnsys/images', os.R_OK) == False:
+                raise OgError('Cannot access /opt/opengnsys/images in read mode, check permissions')
+
             image_path = f'/opt/opengnsys/images/{name}.img'
+
         self._restore_image(image_path, devpath)
 
     def _restore_image_tiptorrent(self, repo, name, devpath):