A missing & was causing an uninitialized
parameter issue and a missing return in
glGetUniformBlockIndex, in the case where
the context is NULL, were causing warnings.

Change-Id: Ifb40583c6d08d185d2e60f96066f1436398318ac
Reviewed-on: https://swiftshader-review.googlesource.com/3436Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>