Fix a crash in the puzzle when not properly initialized

src/app/qgisapp.cpp

@@ -1341,8 +1341,8 @@ QgisApp::QgisApp( QSplashScreen *splash, bool restorePlugins, bool skipVersionCh
   mCentralContainer->insertWidget( 2, puzzleWidget );
   connect( mCoordsEdit, &QgsStatusBarCoordinatesWidget::weAreBored, this, [ this, puzzleWidget ]
   {
-    puzzleWidget->letsGetThePartyStarted();
-    mCentralContainer->setCurrentIndex( 2 );
+    if ( puzzleWidget->letsGetThePartyStarted() )
+      mCentralContainer->setCurrentIndex( 2 );
   } );
   connect( puzzleWidget, &QgsPuzzleWidget::done, this, [ this ]
   {

src/app/qgspuzzlewidget.cpp

@@ -80,6 +80,9 @@ QgsPuzzleWidget::QgsPuzzleWidget( QgsMapCanvas *canvas )
 
 void QgsPuzzleWidget::mousePressEvent( QMouseEvent *event )
 {
+  if ( mTileWidth == 0 || mTileHeight == 0 )
+    return;  // not initialized
+
   int idxEmpty = findEmpty( mPositions );
   int rEmpty = idxEmpty / mSize;
   int cEmpty = idxEmpty % mSize;
@@ -107,12 +110,17 @@ void QgsPuzzleWidget::mousePressEvent( QMouseEvent *event )
   }
 }
 
-void QgsPuzzleWidget::letsGetThePartyStarted()
+bool QgsPuzzleWidget::letsGetThePartyStarted()
 {
   mPositions.clear();
   delete mScene;
   mItems.clear();
   mTextItems.clear();
+  mTileWidth = 0;
+  mTileHeight = 0;
+
+  if ( !mCanvas->layerCount() )
+    return false;
 
   mScene = new QGraphicsScene;
 
@@ -168,6 +176,7 @@ void QgsPuzzleWidget::letsGetThePartyStarted()
   updateTilePositions();
 
   setScene( mScene );
+  return true;
 }
 
 void QgsPuzzleWidget::updateTilePositions()

src/app/qgspuzzlewidget.h

@@ -27,15 +27,14 @@ class QgsPuzzleWidget : public QGraphicsView
   public:
     explicit QgsPuzzleWidget( QgsMapCanvas *canvas = nullptr );
 
+    bool letsGetThePartyStarted();
+
   protected:
     void mousePressEvent( QMouseEvent *event ) override;
 
   signals:
     void done();
 
-  public slots:
-    void letsGetThePartyStarted();
-
   private:
     void updateTilePositions();