qmdiSplitTab: double click open new document on correct tab (#132)

When double clicking the empty area of a tabbar, a new document is
created. Currently, the active tab would get a new tab. What happes if
you click a non active split? The document is opened on the wrong place.

This fixes it. Similar to what has been done in https://github.com/
diegoiast/qtedit4/commit/d46a2c6060d0780ef2bb0bdc8ec8c61df23a5bc2

closes #132

Author: diegoiast

src/widgets/qmdiSplitTab.cpp

@@ -68,7 +68,10 @@ qmdiSplitTab::qmdiSplitTab(QWidget *parent) : SplitTabWidget(parent) {
     connect(this, &SplitTabWidget::emptyAreaDoubleClicked, this,
             [this](QTabWidget *tabWidget, const QPoint &) {
                 auto manager = dynamic_cast<PluginManager *>(this->parent());
-                if (manager) {
+                if (tabWidget) {
+                    updateCurrentTabWidget(tabWidget);
+                }
+                if (tabWidget && manager) {
                     emit manager->newFileRequested(tabWidget->tabBar());
                 }
             });