[FileTransferJob] Fix division by null and use elapsed timer

When sending multiple files from my phone to my PC, kdeconnectd usually received a SIGFPE.
To get the transfer speed it divides the number of bytes received by the elapsed time which can be zero.

Also, since we're only interested in the time that has elapsed, use QElapsedTimer,
which is exactly for this. QTime::elapsed() also needs to take into account potentially
ocurred timezone or DST changes.

REVIEW: 128861

core/filetransferjob.cpp

@@ -80,7 +80,7 @@ void FileTransferJob::doStart()
 void FileTransferJob::startTransfer()
 {
     setProcessedAmount(Bytes, 0);
-    mTime = QTime::currentTime();
+    mTimer.start();
     description(this, i18n("Receiving file over KDE Connect"),
                         { i18nc("File transfer origin", "From"), mFrom },
                         { i18nc("File transfer destination", "To"), mDestination.toLocalFile() });
@@ -91,7 +91,11 @@ void FileTransferJob::startTransfer()
 
     connect(mReply, &QNetworkReply::uploadProgress, this, [this](qint64 bytesSent, qint64 /*bytesTotal*/) {
         setProcessedAmount(Bytes, bytesSent);
-        emitSpeed(bytesSent/mTime.elapsed());
+
+        const auto elapsed = mTimer.elapsed();
+        if (elapsed > 0) {
+            emitSpeed(bytesSent / elapsed);
+        }
     });
     connect(mReply, static_cast<void (QNetworkReply::*)(QNetworkReply::NetworkError)>(&QNetworkReply::error),
             this, &FileTransferJob::transferFailed);

core/filetransferjob.h

@@ -24,8 +24,8 @@
 
 #include <KJob>
 
+#include <QElapsedTimer>
 #include <QIODevice>
-#include <QTime>
 #include <QSharedPointer>
 #include <QUrl>
 #include <QNetworkReply>
@@ -69,7 +69,7 @@ private:
     QNetworkReply* mReply;
     QString mFrom;
     QUrl mDestination;
-    QTime mTime;
+    QElapsedTimer mTimer;
     qulonglong mSpeedBytes;
     qint64 mWritten;
 };