Add nullptr check for captureListener in captureScreenCommon

RegionSamplingThread::captureSample intentionally passes null, which is
already checked for below, but missing in this failure case of
`!renderArea`

Bug: 259021062
Test: presubmits (cost/benefit ratio of adding a new test for this seems
high, given current testing flows and simplicity of change)

Change-Id: I460539404be7a7ae434812aa1f583bba6247a812
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 992760f..581dd13 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -6416,8 +6416,10 @@
                 std::unique_ptr<RenderArea> renderArea = renderAreaFuture.get();
                 if (!renderArea) {
                     ALOGW("Skipping screen capture because of invalid render area.");
-                    captureResults.fenceResult = base::unexpected(NO_MEMORY);
-                    captureListener->onScreenCaptureCompleted(captureResults);
+                    if (captureListener) {
+                        captureResults.fenceResult = base::unexpected(NO_MEMORY);
+                        captureListener->onScreenCaptureCompleted(captureResults);
+                    }
                     return ftl::yield<FenceResult>(base::unexpected(NO_ERROR)).share();
                 }