[LyX/master] Fix the partial patch for #9740 (XeTeX with TeX fonts), part 2.

[Günter Milde]

commit 2aa65fdc8d2cde1ba863173c837c2855a4916d13
Author: Günter Milde <mi...@lyx.org>
Date:   Mon Oct 26 00:51:38 2015 +0100

    Fix the partial patch for #9740 (XeTeX with TeX fonts), part 2.

diff --git a/src/Buffer.cpp b/src/Buffer.cpp
index 73d2007..ae06ff8 100644
--- a/src/Buffer.cpp
+++ b/src/Buffer.cpp
@@ -1675,7 +1675,7 @@ void Buffer::writeLaTeXSource(otexstream & os,
 
        // XeTeX with TeX fonts is only safe with ASCII encoding,
        // See #9740 and FIXME in BufferParams::encoding()
-       if (params().useNonTeXFonts && (runparams.flavor == 
OutputParams::XETEX))
+       if (!params().useNonTeXFonts && (runparams.flavor == 
OutputParams::XETEX))
                runparams.encoding = encodings.fromLyXName("ascii");
 
        // If we are compiling a file standalone, even if this is the