getDisplayDecorationSupport test: allow errors

Allow getDisplayDecorationSupport to return an error, and treat that as
unsupported. This allows Cuttlefish, which, with
I91105fc3345dbd75aeb0b102f3f0138fa33120c0, returns Unsupported, to pass
the test.

Bug: 209458568
Test: this
Change-Id: I8e17d3c0ca0ac4eacb0b5e4c8ae540f271e68a23
diff --git a/graphics/composer/aidl/android/hardware/graphics/composer3/vts/functional/VtsHalGraphicsComposer3_TargetTest.cpp b/graphics/composer/aidl/android/hardware/graphics/composer3/vts/functional/VtsHalGraphicsComposer3_TargetTest.cpp
index f327381..35242c2 100644
--- a/graphics/composer/aidl/android/hardware/graphics/composer3/vts/functional/VtsHalGraphicsComposer3_TargetTest.cpp
+++ b/graphics/composer/aidl/android/hardware/graphics/composer3/vts/functional/VtsHalGraphicsComposer3_TargetTest.cpp
@@ -1627,10 +1627,8 @@
 
         const auto [error, support] =
                 mComposerClient->getDisplayDecorationSupport(display.getDisplayId());
-        EXPECT_TRUE(error.isOk());
 
-        const auto format =
-                support ? support->format
+        const auto format = (error.isOk() && support) ? support->format
                         : aidl::android::hardware::graphics::common::PixelFormat::RGBA_8888;
         const auto decorBuffer = allocate(static_cast<::android::PixelFormat>(format));
         ASSERT_NE(nullptr, decorBuffer);