[SPR-11126] problem converting empty parameter to List

In connection with "[SPR-11126] problem converting empty parameter to List",
the resolveName(String, MethodParameter, NativeWebRequest) method
in the RequestParamMethodArgumentResolver.java has been slightly chagned.
In case that MethodParameter is related to List type,
String[](with legnth 1) value will be returned itself
without being changed to String.

Thank you.

Issue: SPR-11126