backends/drm: check egl config before creating gbm surface

src/backends/drm/egl_gbm_backend.cpp

@@ -291,7 +291,7 @@ bool EglGbmBackend::prefer10bpc() const
 
 EGLConfig EglGbmBackend::config(uint32_t format) const
 {
-    return m_configs[format];
+    return m_configs.value(format, EGL_NO_CONFIG_KHR);
 }
 
 QSharedPointer<DrmPipelineLayer> EglGbmBackend::createDrmPipelineLayer(DrmPipeline *pipeline)

src/backends/drm/egl_gbm_layer.cpp

@@ -200,6 +200,9 @@ bool EglGbmLayer::createGbmSurface(uint32_t format, const QVector<uint64_t> &mod
 
     const auto size = m_pipeline->bufferSize();
     const auto config = m_eglBackend->config(format);
+    if (config == EGL_NO_CONFIG_KHR) {
+        return false;
+    }
 
     QSharedPointer<GbmSurface> gbmSurface;
 #if HAVE_GBM_BO_GET_FD_FOR_PLANE