Fix potential crash in document saving

Probably doesn't happen very often since most of the times people don't save while rendering is still happening
but if that is the case we need to wait for all the rendering to finish otherwise we remove the document
from under the render thread feet and bad things happen

core/document.cpp

@@ -2118,6 +2118,33 @@ void DocumentPrivate::loadSyncFile( const QString & filePath )
             m_pagesVector[i]->setSourceReferences( refRects.at(i) );
 }
 
+void DocumentPrivate::clearAndWaitForRequests()
+{
+    m_pixmapRequestsMutex.lock();
+    QLinkedList< PixmapRequest * >::const_iterator sIt = m_pixmapRequestsStack.constBegin();
+    QLinkedList< PixmapRequest * >::const_iterator sEnd = m_pixmapRequestsStack.constEnd();
+    for ( ; sIt != sEnd; ++sIt )
+        delete *sIt;
+    m_pixmapRequestsStack.clear();
+    m_pixmapRequestsMutex.unlock();
+
+    QEventLoop loop;
+    bool startEventLoop = false;
+    do
+    {
+        m_pixmapRequestsMutex.lock();
+        startEventLoop = !m_executingPixmapRequests.isEmpty();
+        m_pixmapRequestsMutex.unlock();
+        if ( startEventLoop )
+        {
+            m_closingLoop = &loop;
+            loop.exec();
+            m_closingLoop = nullptr;
+        }
+    }
+    while ( startEventLoop );
+}
+
 Document::Document( QWidget *widget )
     : QObject( nullptr ), d( new DocumentPrivate( this ) )
 {
@@ -2533,29 +2560,7 @@ void Document::closeDocument()
     d->m_scripter = nullptr;
 
      // remove requests left in queue
-    d->m_pixmapRequestsMutex.lock();
+    d->clearAndWaitForRequests();
-    QLinkedList< PixmapRequest * >::const_iterator sIt = d->m_pixmapRequestsStack.constBegin();
-    QLinkedList< PixmapRequest * >::const_iterator sEnd = d->m_pixmapRequestsStack.constEnd();
-    for ( ; sIt != sEnd; ++sIt )
-        delete *sIt;
-    d->m_pixmapRequestsStack.clear();
-    d->m_pixmapRequestsMutex.unlock();
-
-    QEventLoop loop;
-    bool startEventLoop = false;
-    do
-    {
-        d->m_pixmapRequestsMutex.lock();
-        startEventLoop = !d->m_executingPixmapRequests.isEmpty();
-        d->m_pixmapRequestsMutex.unlock();
-        if ( startEventLoop )
-        {
-            d->m_closingLoop = &loop;
-            loop.exec();
-            d->m_closingLoop = nullptr;
-        }
-    }
-    while ( startEventLoop );
 
     if ( d->m_fontThread )
     {
@@ -4356,6 +4361,8 @@ bool Document::swapBackingFile( const QString &newFileName, const QUrl &url )
     // Save metadata about the file we're about to close
     d->saveDocumentInfo();
 
+    d->clearAndWaitForRequests();
+
     qCDebug(OkularCoreDebug) << "Swapping backing file to" << newFileName;
     QVector< Page * > newPagesVector;
     Generator::SwapBackingFileResult result = genIt->generator->swapBackingFile( newFileName, newPagesVector );

core/document_p.h

@@ -202,6 +202,8 @@ class DocumentPrivate
         // For sync files
         void loadSyncFile( const QString & filePath );
 
+        void clearAndWaitForRequests();
+
         // member variables
         Document *m_parent;
         QPointer<QWidget> m_widget;