Debugger: Always switch on central widget when entering debug mode

This is not exactly what the linked task complained about, but
solves the issue. Disabling the central editor is rarely useful
(it can be limited to three lines in height) but still temporarily
possible with this patch.

Task-number: QTCREATORBUG-25315
Change-Id: I18182e11d7d3e2167a24a340ab1ae7222009b8c9
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/debugger/debuggermainwindow.cpp

@@ -969,6 +969,8 @@ void Perspective::rampUpAsCurrent()
     theMainWindow->d->setCurrentPerspective(this);
     QTC_ASSERT(theMainWindow->d->m_currentPerspective == this, return);
 
+    theMainWindow->showCentralWidget(true);
+
     d->populatePerspective();
 
     theMainWindow->d->updatePerspectiveChooserWidth();