Fixed the issue why rayrend to print out of error message.
Fixed the issue why rayrend to print out of error message.

cudaGraphicsGLRegisterBuffer will only work properly, if the
associated gl buffer has dimensions > 0. Otherwise, it will
return a NULL pointer as graphics resource.

git-svn-id: a0a066a1d7ce87c7a04dae20f169ad0cd8bda35d@1009 04231f92-3938-0410-9931-e931ac552b4f

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