Fix initialValue block setting

[wesleybl]

This fixes initialValue block setting in two situations:

• When the previous block is an empty block:

In this situation, only the onChangeBlock method was called, which does not call the _applyBlockInitialValue method. Then we call the _applyBlockInitialValue method before calling onChangeBlock.

• When the previous block is not an empty block:

In this situation, the insertBlock method is called. But it passed the id of the previous block to the _applyBlockInitialValue method, instead of the id of the new created block.

fixes #5971

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