Use QSaveFile on file write (LMMS#6107)

Updating to use the recommended method QSaveFile instead of QFile.
Hopefully fix issue where LMMS in rare occasions would produce empty
files on save. 

---------

Co-authored-by: Kevin Zander <[email protected]>

src/core/DataFile.cpp

@@ -35,6 +35,7 @@
 #include <QFileInfo>
 #include <QDir>
 #include <QMessageBox>
+#include <QSaveFile>
 
 #include "base64.h"
 #include "ConfigManager.h"
@@ -379,12 +380,12 @@ bool DataFile::writeFile(const QString& filename, bool withResources)
 		}
 	}
 
-	QFile outfile (fullNameTemp);
+	QSaveFile outfile(fullNameTemp);
 
 	if (!outfile.open(QIODevice::WriteOnly | QIODevice::Truncate))
 	{
 		showError(SongEditor::tr("Could not write file"),
-			SongEditor::tr("Could not open %1 for writing. You probably are not permitted to"
+			SongEditor::tr("Could not open %1 for writing. You probably are not permitted to "
 				"write to this file. Please make sure you have write-access to "
 				"the file and try again.").arg(fullName));
 
@@ -405,30 +406,29 @@ bool DataFile::writeFile(const QString& filename, bool withResources)
 		write( ts );
 	}
 
-	outfile.close();
-
-	// make sure the file has been written correctly
-	if( QFileInfo( outfile.fileName() ).size() > 0 )
+	if (!outfile.commit())
 	{
-		if( ConfigManager::inst()->value( "app", "disablebackup" ).toInt() )
-		{
-			// remove current file
-			QFile::remove( fullName );
-		}
-		else
-		{
-			// remove old backup file
-			QFile::remove( fullNameBak );
-			// move current file to backup file
-			QFile::rename( fullName, fullNameBak );
-		}
-		// move temporary file to current file
-		QFile::rename( fullNameTemp, fullName );
+		showError(SongEditor::tr("Could not write file"),
+			SongEditor::tr("An unknown error has occured and the file could not be saved."));
+		return false;
+	}
 
-		return true;
+	if (ConfigManager::inst()->value("app", "disablebackup").toInt())
+	{
+		// remove current file
+		QFile::remove(fullName);
 	}
+	else
+	{
+		// remove old backup file
+		QFile::remove(fullNameBak);
+		// move current file to backup file
+		QFile::rename(fullName, fullNameBak);
+	}
+	// move temporary file to current file
+	QFile::rename(fullNameTemp, fullName);
 
-	return false;
+	return true;
 }