#1588 If the SC_MOD_INSERTCHECK notification handler sends an empty string via SCI_CHANGEINSERTION, you should not attempt to insert anything.

[Schreiner]

If a decision is made in an SC_MOD_INSERTCHECK notification handler to prevent the desired insertion, an empty string can be sent via SCI_CHANGEINSERTION, but no attempt should then be made to insert it. Currently, this results in an empty undo entry and thus also changes the savepoint. Therefore, it would be preferable to simply do the same as when passing insertLength = 0 to Document::InsertString.

[Neil Hodgson]

Committed equivalent code with [54d811].