Crash in Tehreer stack on '\n' character

[heybdj]

Given the input string "A\nB", the Tehreer stack will crash when creating the second line of the run. The fix is to pass the paragraph starting offset to SBParagraphCreateLine(...) here:

https://github.com/unicode-org/text-rendering-tests/blob/f9535a12551d2fb25d8288547692271ebef38c35/src/fonttest/tehreerstack_line.cpp#L152

The fix should look like this:

SBLineRef line = SBParagraphCreateLine(paragraph, paraStart, paraLen);