[rasapi32] fix tests on platforms winme and some win98

[Stefan Leichter]

This patch fixes 
http://test.winehq.org/data/5f727cb2afbfafc3b396cf4902e55ca95dbc69d5/98_fg-win98/rasapi32:rasapi.html
http://test.winehq.org/data/de92617b3ec1501a2a56f6262d9653f502a5b331/me_gQd/rasapi32:rasapi.html

Changelog
---------
	skip the RasEnumDevicesA tests when the initial call to the function doesn't 
return useful data
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