Delay modal dialogs until next event loop iteration

Showing a modal dialog with its own event loop while painting a GL view
can break the rendering state. This commits changes two dialogs that
could potentially pop up during rendering so that they are only shown in
the next iteration of the event loop, outside of painting.

common/src/PreferenceManager.cpp

@@ -38,6 +38,7 @@
 #include <QMessageBox>
 #include <QStandardPaths>
 #include <QStringBuilder>
+#include <QTimer>
 
 #include <string>
 #include <vector>
@@ -427,9 +428,11 @@ void AppPreferenceManager::showErrorAndDisableFileReadWrite(
       .arg(m_preferencesFilePath)
       .arg(suggestion);
 
-  auto dialog =
-    QMessageBox(QMessageBox::Icon::Critical, tr("TrenchBroom"), message, QMessageBox::Ok);
-  dialog.exec();
+  QTimer::singleShot(0, [=] {
+    auto dialog = QMessageBox(
+      QMessageBox::Icon::Critical, tr("TrenchBroom"), message, QMessageBox::Ok);
+    dialog.exec();
+  });
 }
 
 /**

common/src/TrenchBroomApp.cpp

@@ -427,7 +427,9 @@ bool TrenchBroomApp::recoverFromException(
   }
   else
   {
-    QMessageBox::critical(nullptr, "TrenchBroom", e.what(), QMessageBox::Ok);
+    QTimer::singleShot(0, [message = e.what()] {
+      QMessageBox::critical(nullptr, "TrenchBroom", message, QMessageBox::Ok);
+    });
     return false;
   }
 }