Source/WebCore: Crash in DeleteSelectionCommand::handleGeneralDelete when attempting...

Source/WebCore: Crash in DeleteSelectionCommand::handleGeneralDelete when attempting to delete the start block
https://bugs.webkit.org/show_bug.cgi?id=77077

Reviewed by Enrica Casucci.

The crash was caused by a missing null check after removing the position out of the start block.
Fixed the bug by adding an early return.

Tests: editing/deleting/delete-start-block.html
       editing/selection/move-into-empty-root-inline-box.html

* editing/DeleteSelectionCommand.cpp:
(WebCore::DeleteSelectionCommand::handleGeneralDelete):

LayoutTests: Crash in previousLinePosition when moving into a root inline box without leaves
https://bugs.webkit.org/show_bug.cgi?id=76812

Reviewed by Enrica Casucci.

Add a regression test for the crash. Unfortunately, we can only test previousLinePosition.

* editing/selection/move-into-empty-root-inline-box-expected.txt: Added.
* editing/selection/move-into-empty-root-inline-box.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@106380 268f45cc-cd09-0410-ab3c-d52691b4dbfc