Fix raytracing example.
Fix raytracing example.

Note to all: please initialize GLSL variables to zero
when necessary :)

jay3sh/vispy,Eric89GXL/vispy,michaelaye/vispy,drufat/vispy,Eric89GXL/vispy,kkuunnddaannkk/vispy,drufat/vispy,QuLogic/vispy,ghisvail/vispy,sh4wn/vispy,kkuunnddaannkk/vispy,hronoses/vispy,bollu/vispy,dchilds7/Deysha-Star-Formation,drufat/vispy,sh4wn/vispy,srinathv/vispy,srinathv/vispy,julienr/vispy,sbtlaarzc/vispy,inclement/vispy,sbtlaarzc/vispy,sbtlaarzc/vispy,julienr/vispy,jdreaver/vispy,sh4wn/vispy,jdreaver/vispy,dchilds7/Deysha-Star-Formation,dchilds7/Deysha-Star-Formation,ghisvail/vispy,RebeccaWPerry/vispy,jdreaver/vispy,michaelaye/vispy,michaelaye/vispy,inclement/vispy,julienr/vispy,bollu/vispy,hronoses/vispy,kkuunnddaannkk/vispy,jay3sh/vispy,Eric89GXL/vispy,bollu/vispy,RebeccaWPerry/vispy,ghisvail/vispy,inclement/vispy,QuLogic/vispy,QuLogic/vispy,RebeccaWPerry/vispy,jay3sh/vispy,hronoses/vispy,srinathv/vispy