Fixed "Repeat last export on save" when using Save All

Due to directly calling Document::save in MainWindow::saveAll, the
DocumentManager::documentSaved signal was not being emitted.

Closes #2969

src/tiled/documentmanager.cpp

@@ -683,6 +683,7 @@ bool DocumentManager::saveDocument(Document *document, const QString &fileName)
 
     QString error;
     if (!document->save(fileName, &error)) {
+        switchToDocument(document);
         QMessageBox::critical(mWidget->window(), QCoreApplication::translate("Tiled::MainWindow", "Error Saving File"), error);
         return false;
     }

src/tiled/mainwindow.cpp

@@ -1176,9 +1176,7 @@ void MainWindow::saveAll()
             mDocumentManager->switchToDocument(document.data());
             if (!mDocumentManager->saveDocumentAs(document.data()))
                 return;
-        } else if (!document->save(fileName, &error)) {
-            mDocumentManager->switchToDocument(document.data());
-            QMessageBox::critical(this, tr("Error Saving File"), error);
+        } else if (!mDocumentManager->saveDocument(document.data(), fileName)) {
             return;
         }
     }