Fix potential deadlock in UI when saving

This was noted as a problem in several issues and it finally occurred to me and I traced it to the fact that a timing issue sometimes allowed the file watcher to trigger a "file changed" alert right when saving starts. I fixed this by moving where the mutex lock is made for saving and preventing database reload during a save operation.

src/core/Database.cpp

@@ -253,9 +253,6 @@ bool Database::saveAs(const QString& filePath, SaveAction action, const QString&
         return false;
     }
 
-    // Prevent destructive operations while saving
-    QMutexLocker locker(&m_saveMutex);
-
     if (filePath == m_data.filePath) {
         // Fail-safe check to make sure we don't overwrite underlying file changes
         // that have not yet triggered a file reload/merge operation.
@@ -270,6 +267,9 @@ bool Database::saveAs(const QString& filePath, SaveAction action, const QString&
     // Clear read-only flag
     m_fileWatcher->stop();
 
+    // Prevent destructive operations while saving
+    QMutexLocker locker(&m_saveMutex);
+
     QFileInfo fileInfo(filePath);
     auto realFilePath = fileInfo.exists() ? fileInfo.canonicalFilePath() : fileInfo.absoluteFilePath();
     bool isNewFile = !QFile::exists(realFilePath);
@@ -463,6 +463,7 @@ bool Database::import(const QString& xmlExportPath, QString* error)
 void Database::releaseData()
 {
     // Prevent data release while saving
+    Q_ASSERT(!isSaving());
     QMutexLocker locker(&m_saveMutex);
 
     if (m_modified) {

src/gui/DatabaseWidget.cpp

@@ -1747,8 +1747,8 @@ bool DatabaseWidget::lock()
 
 void DatabaseWidget::reloadDatabaseFile()
 {
-    // Ignore reload if we are locked or currently editing an entry or group
-    if (!m_db || isLocked() || isEntryEditActive() || isGroupEditActive()) {
+    // Ignore reload if we are locked, saving, or currently editing an entry or group
+    if (!m_db || isLocked() || isEntryEditActive() || isGroupEditActive() || isSaving()) {
         return;
     }