gluon-luci-admin: fix SSH keys being removed when a password is set

package/gluon-luci-admin/files/usr/lib/lua/luci/model/cbi/admin/remote.lua

@@ -51,9 +51,11 @@ if fs.access("/etc/config/dropbear") then
   end
 
   function keys.remove(self, section)
+    if keys:formvalue("_keys") then
       fs.remove("/etc/dropbear/authorized_keys")
     end
   end
+end
 
 local m2 = Map("system", "Passwort")
 m2.submit = "Speichern"