Can return -1

.Net Framework 4.7.2, textbox, calling GetLineFromCharacterIndex from LostFocus handler I'm getting -1. There's no mention of any special cases in the documentation

---
#### Document Details

⚠ *Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.*

* ID: 9840ccb2-55de-b00d-9a87-5054a19b90f4
* Version Independent ID: c5da7d3d-fa67-0eed-fad0-3c9c7695f768
* Content: [TextBox.GetLineIndexFromCharacterIndex(Int32) Method (System.Windows.Controls)](https://docs.microsoft.com/en-us/dotnet/api/system.windows.controls.textbox.getlineindexfromcharacterindex?redirectedfrom=MSDN&view=netframework-4.7.2#System_Windows_Controls_TextBox_GetLineIndexFromCharacterIndex_System_Int32_)
* Content Source: [xml/System.Windows.Controls/TextBox.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Windows.Controls/TextBox.xml)
* Product: **dotnet-api**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **dotnetcontent**