https://bugs.kde.org/show_bug.cgi?id=501181

(This is a minimal backport of https://invent.kde.org/plasma/kwin/-/commit/e652bdd3118fa55563caf0125deb0999f5ebd503,
but given the next release is on Tuesday, let's just go with the thing that
is confirmed to work.)

From d63e308604d6b45f5c572acd4f299e2c5cfbab44 Mon Sep 17 00:00:00 2001
From: Mike Lothian <mike@fireburn.co.uk>
Date: Fri, 7 Mar 2025 15:24:00 +0000
Subject: [PATCH] Quick fix

---
 src/backends/drm/drm_gpu.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/backends/drm/drm_gpu.cpp b/src/backends/drm/drm_gpu.cpp
index 4599b3d..a47f5ce 100644
--- a/src/backends/drm/drm_gpu.cpp
+++ b/src/backends/drm/drm_gpu.cpp
@@ -443,6 +443,10 @@ DrmPipeline::Error DrmGpu::testPendingConfiguration()
 
 DrmPipeline::Error DrmGpu::testPipelines()
 {
+    if (m_pipelines.isEmpty()) {
+        // nothing to do
+        return DrmPipeline::Error::None;
+    }
     QList<DrmPipeline *> inactivePipelines;
     std::copy_if(m_pipelines.constBegin(), m_pipelines.constEnd(), std::back_inserter(inactivePipelines), [](const auto pipeline) {
         return pipeline->enabled() && !pipeline->active();
-- 
2.48.1