Fix asserts for GetReadbackBufferFenceInactive

If there's no readback buffer, then the status is NOT ok(), and the
returned fence must be -1.

Bug: 213493262
Test: VtsHalGraphicsComposer3_TargetTest
Change-Id: Iff1b6e04126bfcc748f0f8d173f63244bfd83be4
diff --git a/graphics/composer/aidl/android/hardware/graphics/composer3/vts/functional/VtsHalGraphicsComposer3_ReadbackTest.cpp b/graphics/composer/aidl/android/hardware/graphics/composer3/vts/functional/VtsHalGraphicsComposer3_ReadbackTest.cpp
index fc527ec..3f1e703 100644
--- a/graphics/composer/aidl/android/hardware/graphics/composer3/vts/functional/VtsHalGraphicsComposer3_ReadbackTest.cpp
+++ b/graphics/composer/aidl/android/hardware/graphics/composer3/vts/functional/VtsHalGraphicsComposer3_ReadbackTest.cpp
@@ -521,8 +521,9 @@
     ndk::ScopedFileDescriptor releaseFence;
     const auto error = mComposerClient->getReadbackBufferFence(mPrimaryDisplay, &releaseFence);
 
-    EXPECT_TRUE(error.isOk());
+    ASSERT_FALSE(error.isOk());
     EXPECT_EQ(IComposerClient::EX_UNSUPPORTED, error.getServiceSpecificError());
+    EXPECT_EQ(-1, releaseFence.get());
 }
 
 TEST_P(GraphicsCompositionTest, ClientComposition) {