Prevent multiple lock requests on Linux

* Fixes #11000

When the screen locks on e.g. gnome we receive multiple independent signals of that, namely the Gnome session manager and the gnome / freedesktop screensaver.

When this happens, this causes multiple "lock database" requests to be issued. The first one correctly shows the question to discard/cancel, but the second one while the first is still asking goes and dismisses the question and then goes to ask it again. The result is it acts like you didn't answer correctly (ie, to cancel) and the database is locked.

src/gui/DatabaseWidget.cpp

@@ -1787,8 +1787,8 @@ bool DatabaseWidget::focusNextPrevChild(bool next)
 
 bool DatabaseWidget::lock()
 {
-    if (isLocked()) {
-        return true;
+    if (isLocked() || m_attemptingLock) {
+        return isLocked();
     }
 
     // Don't try to lock the database while saving, this will cause a deadlock
@@ -1797,6 +1797,8 @@ bool DatabaseWidget::lock()
         return false;
     }
 
+    m_attemptingLock = true;
+
     emit databaseLockRequested();
 
     // Force close any modal widgets associated with this widget
@@ -1821,6 +1823,7 @@ bool DatabaseWidget::lock()
                                            MessageBox::Discard | MessageBox::Cancel,
                                            MessageBox::Cancel);
         if (result == MessageBox::Cancel) {
+            m_attemptingLock = false;
             return false;
         }
     }
@@ -1847,9 +1850,11 @@ bool DatabaseWidget::lock()
                                                MessageBox::Save);
             if (result == MessageBox::Save) {
                 if (!save()) {
+                    m_attemptingLock = false;
                     return false;
                 }
             } else if (result == MessageBox::Cancel) {
+                m_attemptingLock = false;
                 return false;
             }
         }
@@ -1881,6 +1886,7 @@ bool DatabaseWidget::lock()
     auto newDb = QSharedPointer<Database>::create(m_db->filePath());
     replaceDatabase(newDb);
 
+    m_attemptingLock = false;
     emit databaseLocked();
 
     return true;

src/gui/DatabaseWidget.h

@@ -305,6 +305,7 @@ private slots:
     QUuid m_entryBeforeLock;
 
     int m_saveAttempts;
+    bool m_attemptingLock = false;
 
     // Search state
     QScopedPointer<EntrySearcher> m_entrySearcher;