glsl: on UBO/SSBOs link error reset the number of active blocks to 0

glsl: on UBO/SSBOs link error reset the number of active blocks to 0

While it's legal to have an active blocks count > 0 on link failure.
Unless we actually assign memory for the blocks array we can end up
segfaulting in calls such as glUniformBlockBinding().

To avoid having to NULL check these api calls we simply reset the
block count to 0 if the array was not created.

Signed-off-by: Andres Gomez <agomez@igalia.com>
Cc: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>