Replace QTC_ASSERT with normal check

Optionspages are called even if they weren't shown.

src/plugins/projectexplorer/toolchainoptionspage.cpp

@@ -532,7 +532,7 @@ QWidget *ToolChainOptionsPage::createPage(QWidget *parent)
 
 void ToolChainOptionsPage::apply()
 {
-    QTC_ASSERT(m_model, return; )
+    if (m_model)
         m_model->apply();
 }