PATCH: Several fixes for SetupInstallServicesFromInfSectionExW

This patch fixes the following issues:
-Check if "sectionname" is NULL at the beginning of the API (and react accordingly) instead going through the whole function. Readability++;
-Check if "sectionname" represents a real section and fail at the very beginning if it is not. This prevents iterating through the fields of a non-existent "sectionname" as we are doing right now.
-Set the proper error (ERROR_SECTION_NOT_FOUND) and return FALSE if "sectionname" does not exist. Tested in 2003SP1.
Kill an unneeded IF-ELSE param-check castle.
-SO basically, this patch forces to fail gracefully when params are wrong and does not touch the rest of the logic.

Also, by checking params, this patch introduces a nice feature:

• It.kills ReactOS boot with "InstallSysSetupInfDevices() failed". This bug has been reported and tracked down in CORE-9406