SearchNode fails with unbalanced tree with next version (ts)

[MatthieuNICOLAS]

While working on the next version, we disabled the balancing of the tree to make debugging easier.
But it shows a new issue: the function searchNode() (called here) can not find the node where to insert the new block and thus returns a null value.

Scenario to reproduce this issue:

• Insert a first block.
• Split this block with a new one.
• Append new blocks to the splitting one until the null exception is thrown.