Fixes an assertion when moving from passthrough to non-passthrough
Without an explicit reconfigure, glfiter won't have created the GL
resources such as the FBO, GL bufferpool, etc and basetransform will
allocate sysmem buffers instead.
There's no need for the jump to an extra thread in most cases, especially
when relying solely on a shader to render. We can use the provided
render_to_target() functions to simplify filter writing.
It performs the exact same operation as videobalance but with opengl shaders and
was tested with glvideomixer by comparing frames from videobalance and
glcolorbalance.
