OCGV: Filter edit chops off first char of filter string passed on command line

[tig]

Or, do

Get-Process | Out-ConsoleGridView -Filter test

This doesn't appear to impact filter functionality, it's just that the first character is not visible. If one backspace to delete all of the filter string, it DOES delete that first char.

[tig]

Turns out this is caused by the logic in _filterField.TextChanged that was serendipitously fixed by the upgrade to Terminal.Gui 1.6 in #153.

So once #153 is merged, this issue will be fixed.

[tig]

I've confirmed this is fixed with the current code in master.

[tig]

Fixed in #166.