drm: dont commit state if renderer is missing

setting certain env vars to force egl implentations makes the render
creation fail on the second gpu. instead of causing a coredump,
safeguard commitState and let the monitor turn blank instead.

src/backend/drm/DRM.cpp

@@ -1400,6 +1400,11 @@ bool Aquamarine::CDRMOutput::commitState(bool onlyTest) {
         return false;
     }
 
+    if (!backend->rendererState.renderer) {
+        backend->backend->log(AQ_LOG_ERROR, "drm: No renderer attached to backend");
+        return false;
+    }
+
     const auto&    STATE     = state->state();
     const uint32_t COMMITTED = STATE.committed;