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This was broken since r1557 when we got rid of some exit calls, but returned
-1 instead which is not a valid HANDLE value.

Corresponding to flashrom svn r1591.
Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Idwer Vollering <vidwer@gmail.com>