XpsSerialization in presentationcore.dll throws System.IO.FileFormatException

[rladuca]

When working with XPS documents WPF will subset fonts in order to reduce their size during embedding. In certain cases, this can result in the font growing during subsetting.

This results in us returning ERR_WOULD_GROW:

wpf/src/Microsoft.DotNet.Wpf/src/DirectWriteForwarder/CPP/TrueTypeSubsetter/TtfDelta/ttfdelta.cpp

Line 920 in e4a212b

errCode = ERR_WOULD_GROW; /* use the original font */

We already know what to do in this case (as the comments in the code above suggest), use the original font. However, we seem to be ignoring that:

wpf/src/Microsoft.DotNet.Wpf/src/DirectWriteForwarder/CPP/TrueTypeSubsetter/truetype.cpp

Lines 105 to 106 in 70da708

	if (errCode != NO_ERROR)
	throw gcnew FileFormatException(sourceUri);

The fix is pretty straightforward, simply copy the font into the result buffer when we detect ERR_WOULD_GROW and return as usual.

[rladuca]

This bug is the vNext port from DTS servicing request 957257.

[rladuca]

Merged this fix via #1513, leaving bug open for tell mode review.