Don't emit pyodbc "no driver" warning for empty URL
Fixed an issue in the pyodbc connector such that a warning about pyodbc
"drivername" would be emitted when using a totally empty URL. Empty URLs
are normal when producing a non-connected dialect object or when using the
"creator" argument to create_engine(). The warning now only emits if the
driver name is missing but other parameters are still present.
Fixes: #5346
Change-Id: I0ee6f5fd5af7faca63bf0d7034410942f40834a8
(cherry picked from commit
29534cf13939c7f7fe59399f12d50df2fcab7a38)