Fix size_table bug during rrb_concat
Fix size_table bug during rrb_concat

This bug happens when one attempts to concatenate two trees, where the
right root is null, the tails have more than the branching factor
elements in total, and and the height has to be increased when pushing
down the tail.

hyPiRion/c-rrb,hyPiRion/c-rrb,hyPiRion/c-rrb,hyPiRion/c-rrb