Coco: fix crash in CocoBuildStep

The bug was reported via Sentry and I could not reproduce it here, but
the immediate cause was clear: m_buildSettings was used when it was
still a null pointer - certainly because CocoBuildStep::display() was
not yet called.

I have added code that prevents this.

Fixes: QTCREATORBUG-32850
Change-Id: I8226e1466870e77749aff276de150b79f75332a4
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/coco/cocobuildstep.cpp

@@ -77,6 +77,8 @@ void CocoBuildStep::buildSystemUpdated()
 
 void CocoBuildStep::onButtonClicked()
 {
+    QTC_ASSERT(m_buildSettings, return);
+
     m_valid = !m_valid;
 
     setSummaryText(Tr::tr("Coco Code Coverage: Reconfiguring..."));
@@ -97,6 +99,8 @@ QWidget *CocoBuildStep::createConfigWidget()
 
 void CocoBuildStep::updateDisplay()
 {
+    QTC_ASSERT(m_buildSettings, return);
+
     if (!cocoSettings().isValid()) {
         setSummaryText("<i>" + Tr::tr("Coco Code Coverage: No working Coco installation.") + "</i>");
         emit setButtonState(false);