Crash: Often "Position not in text" exceptions when working with text.

[boyan]

1. Create a new book.
2. Insert a text frame.
3. Type some text.
4. Delete all the text.
5. Type some new text.
6. Position the caret before the last character and hit delete. -> crash

Can also be invoked in various situations, hard to reproduce every time, makes text unusable.

[boyan]

finishing the bug report

[boyan]

starting design

[boyan]

The bug is caused by having an invalid position in an edge of the layout. It happens in different situations and can be hardly tracked (and reproduced). This is not a fix but a workaround that reduces throwing exceptions to a minimum.

Here are few things that cause the bug:

1. isPresent() method of NaiveNavigator needs an additional check - when there is no text at all, the pre and post positions of the docUnit are still present and the method should return true.
2. A check for valid positions is needed in the draw method of the EdgeKind.
3. Logger messages in HotTextLayout that print invalid edges cause an exception to be thrown. Text manipulation is possible even with such edges so these loggers will be commented out.
4. Cutting text does not set the caret and mark position which leads to errors when trying to type.

These have been fixed in the following changeset: [5199]. There are still rare occasions when the exception is thrown but text now is much more usable.

[meddle]

Merged in [5217]. The error is not permanently fixed but in most cases the condition is better.