Valgrind error patch in gr_RenderInfo.cpp

Hi,

I'm posting this patch, so that people (mostly Tomas) review it because
I'm not familiar with the inner guts of the code.

Basically, the if() was reading outside the array bounds so I added a
condition to prevent this and makes Valgrind happy (complaining about
test depending on unitilized data).

If you feel it is safe, either commit it or let me know.

Thanks.

Hub

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