[LyX/master] Remove spurious error "QFileSystemWatcher::removePath: path is empty"

[Guillaume MM]

commit 974d33ad01098fbb68e4391264b0456769a96b6a
Author: Guillaume MM <g...@lyx.org>
Date:   Mon May 1 00:02:10 2017 +0200

    Remove spurious error "QFileSystemWatcher::removePath: path is empty"
---
 src/support/FileMonitor.cpp |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/src/support/FileMonitor.cpp b/src/support/FileMonitor.cpp
index f1446a3..30a4170 100644
--- a/src/support/FileMonitor.cpp
+++ b/src/support/FileMonitor.cpp
@@ -100,6 +100,8 @@ FileMonitorGuard::FileMonitorGuard(string const & filename,
                                    QFileSystemWatcher * qwatcher)
        : filename_(filename), qwatcher_(qwatcher), exists_(true)
 {
+       if (filename.empty())
+               return;
        QObject::connect(qwatcher, SIGNAL(fileChanged(QString const &)),
                         this, SLOT(notifyChange(QString const &)));
        if (qwatcher_->files().contains(toqstr(filename)))
@@ -111,12 +113,15 @@ FileMonitorGuard::FileMonitorGuard(string const & 
filename,
 
 FileMonitorGuard::~FileMonitorGuard()
 {
-       qwatcher_->removePath(toqstr(filename_));
+       if (!filename_.empty())
+               qwatcher_->removePath(toqstr(filename_));
 }
 
 
 void FileMonitorGuard::refresh()
 {
+       if (filename_.empty())
+               return;
        QString const qfilename = toqstr(filename_);
        if(!qwatcher_->files().contains(qfilename)) {
                bool exists = QFile(qfilename).exists();