validate end positions before calling lineAt

[HookyQR]

This stops the multitude of exceptions thrown when deleting the last line of text in the editor.

[shardulm94]

Hi @HookyQR,
Thanks for your pull request. I should be able to review and merge this in the next few days.

[shardulm94]

@HookyQR Can you help me reproduce this issue? I was not able to reproduce it.

[HookyQR]

• Open a new window.
• Toggle Dev Tools (Help -> Toggle Dev Tools)
• In the editor window, hit Enter, then backspace.

Result (In Dev tools console):

shell.ts:428
Illegal value for `line`: Error: Illegal value for `line`
    at t.lineAt (/Applications/Visual Studio Code.app/Contents/Resources/app/out/vs/workbench/node/extensionHostProcess.js:11:15517)
    at Object._document.lineAt (/Applications/Visual Studio Code.app/Contents/Resources/app/out/vs/workbench/node/extensionHostProcess.js:11:14525)
    at TrailingSpaces.matchTrailingSpaces (/Users/hooky/.vscode/extensions/shardulm94.trailing-spaces-0.2.10/out/src/trailing-spaces/trailing-spaces.js:231:95)
    at /Users/hooky/.vscode/extensions/shardulm94.trailing-spaces-0.2.10/out/src/trailing-spaces/trailing-spaces.js:72:27
    at e.invoke (/Applications/Visual Studio Code.app/Contents/Resources/app/out/vs/workbench/node/extensionHostProcess.js:6:13653)
    at e.fire (/Applications/Visual Studio Code.app/Contents/Resources/app/out/vs/workbench/node/extensionHostProcess.js:6:15829)
    at t.$acceptModelChanged (/Applications/Visual Studio Code.app/Contents/Resources/app/out/vs/workbench/node/extensionHostProcess.js:11:13505)
    at t.e.handle (/Applications/Visual Studio Code.app/Contents/Resources/app/out/vs/workbench/node/extensionHostProcess.js:10:22905)
    at s (/Applications/Visual Studio Code.app/Contents/Resources/app/out/vs/workbench/node/extensionHostProcess.js:7:30449)
    at p (/Applications/Visual Studio Code.app/Contents/Resources/app/out/vs/workbench/node/extensionHostProcess.js:7:31126)

[shardulm94]

Thanks again for the pull! The update has been published.