confighelper: don't overwrite option tracking

Its possible for any component to request a configuration
option from another component.  Don't overwrite the
inital value stored.

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

moonraker/confighelper.py

@@ -151,6 +151,7 @@ class ConfigHelper:
                     f"configuration, see {help} for detailed documentation."
                 )
             self._check_option(option, val, above, below, minval, maxval)
+        if option not in self.parsed[section]:
             if (
                 val is None or
                 isinstance(val, (int, float, bool, str, dict, list))