fix lineCharacterOffset generating a negative value

[maverck]

lineCharacterOffset = lineText.length - 1;

this line results in a negative value sometimes? and the extension crashes and no longer provides completion. I clamped the value so it can't be negative.

[ghedwards]

Can this be merged , this seems to prevent issues where I have to restart VSCode to resolve them currently

[ghedwards]

Ping!? could this be merged ?

[pczarn2]

@KamasamaK just wondering if you saw this merge request?

[garethedwards-tass]

This is fixed in my latest fork https://github.com/garethedwards-tass/vscode-cfml turns out the fix was more involved than this specific change