Fix OSX bug with glyphs culling geometry shader

Apple driver does not fully respect GLSL specifications:

A default value for the stream can be set with:

layout(stream = 2) out;

All following out variables will use stream 2 unless they specify a stream. The default can be changed later. The initial default is 0.

Using this feature results in a compilation error of the shader.
The workaround is to specify the stream for each output variable.