[LyX/master] Fix warnings.

[Richard Kimberly Heck]

commit 1948391a94e0486f1d16df1e7d49ec4cd8724ad7
Author: Richard Kimberly Heck <rikiheck at lyx.org>
Date:   Fri Feb 28 00:07:53 2020 -0500

    Fix warnings.
---
 src/frontends/qt/ButtonController.cpp |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/frontends/qt/ButtonController.cpp b/src/frontends/qt/ButtonController.cpp
index c8644ab..d2910c8 100644
--- a/src/frontends/qt/ButtonController.cpp
+++ b/src/frontends/qt/ButtonController.cpp
@@ -47,7 +47,7 @@ static void setWidgetEnabled(QWidget * obj, bool enabled)
 class CheckedLineEdit
 {
 public:
-	CheckedLineEdit(QLineEdit * input, QWidget * label = 0);
+	CheckedLineEdit(QLineEdit * input, QWidget * label = nullptr);
 	bool check() const;
 
 private:
@@ -93,7 +93,8 @@ public:
 	typedef QList<CheckedLineEdit> CheckedWidgetList;
 
 	Private()
-		: okay_(0), apply_(0), cancel_(0), restore_(0), auto_apply_(0), default_(0),
+		: okay_(nullptr), apply_(nullptr), cancel_(nullptr),
+			restore_(nullptr), auto_apply_(nullptr), default_(nullptr),
 			policy_(ButtonPolicy::IgnorantPolicy)
 	{}