glsl: don't lose uniform values when falling back to full compile

glsl: don't lose uniform values when falling back to full compile

Here we skip the recreation of uniform storage if we are relinking
after a cache miss. This is improtant because uniform values may
have already been set by the application and we don't want to reset
them.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>