[LyX/2.3.x] Set preamble tab stop to 4 chars.

[Richard Heck]

commit d1fa6f10e595643c7a4220654c6eaee9d8920251
Author: Richard Heck <rgh...@lyx.org>
Date:   Sun Apr 1 22:18:37 2018 -0400

    Set preamble tab stop to 4 chars.
---
 src/frontends/qt4/GuiDocument.cpp |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/src/frontends/qt4/GuiDocument.cpp 
b/src/frontends/qt4/GuiDocument.cpp
index f5af06e..0ff70a8 100644
--- a/src/frontends/qt4/GuiDocument.cpp
+++ b/src/frontends/qt4/GuiDocument.cpp
@@ -473,6 +473,10 @@ PreambleModule::PreambleModule(QWidget * parent)
        connect(findButtonPB, SIGNAL(clicked()), this, SLOT(findText()));
        connect(findLE, SIGNAL(returnPressed()), this, SLOT(findText()));
        checkFindButton();
+       // 
https://stackoverflow.com/questions/13027091/how-to-override-tab-width-in-qt
+       const int tabStop = 4;
+       QFontMetrics metrics(preambleTE->currentFont());
+       preambleTE->setTabStopWidth(tabStop * metrics.width(' '));
 }