Fix odbc:param_query/3 and odbc:param_query/4.

Issue: Calling odbc:param_query/3 and odbc:param_query/4 with unparameterized query string and empty parameters list causes error in pattern matching in function param_values/1.

This patch fixes this problem and allow to do things such as
> odbc:param_query(ConRef, "select * from some_table", []).