Fix Cycles area light using MIS when the spread is zero

area light with zero spread was introduced in bf18032977. Such paths can
only be sampled with NEE, so MIS should not be used.
This fixes the discrepancy when Direct Light Sampling is set to MIS or NEE.

Pull Request: #118584

intern/cycles/scene/light.cpp

@@ -1331,7 +1331,7 @@ void LightManager::device_update_lights(Device *device, DeviceScene *dscene, Sce
 
       float3 dir = safe_normalize(light->get_dir());
 
-      if (light->use_mis && area != 0.0f) {
+      if (light->use_mis && area != 0.0f && light->spread > 0.0f) {
         shader_id |= SHADER_USE_MIS;
       }
 

tests/data

@@ -1 +1 @@
-Subproject commit 582cf6fcb4e7456a6d29eb016280943646e6bc68
+Subproject commit 6dd81d3f24ec18cec2ab70d1c4159be3900ccd55