No crash from AHardwareBuffer_unlock on NULL fence

The API document states: "If fence is not NULL then it will be set to a
file descriptor that is signaled when all pending work on the buffer is
completed." As it's too late to change the document, we should probably
update the implement and use GraphicsBuffer::unlock under the hood.

Bug: 62302267
Test: Build, AHardware CTS
Change-Id: Ic0fac5d7addfba67baaa1b5d7c221fc25d02df56
(cherry picked from commit 6cdbb537105b663572e71afe06bde1164fc215f3)
diff --git a/libs/nativewindow/AHardwareBuffer.cpp b/libs/nativewindow/AHardwareBuffer.cpp
index c0602e7..2f4b996 100644
--- a/libs/nativewindow/AHardwareBuffer.cpp
+++ b/libs/nativewindow/AHardwareBuffer.cpp
@@ -134,7 +134,10 @@
     if (!buffer) return BAD_VALUE;
 
     GraphicBuffer* gBuffer = AHardwareBuffer_to_GraphicBuffer(buffer);
-    return gBuffer->unlockAsync(fence);
+    if (fence == nullptr)
+        return gBuffer->unlock();
+    else
+        return gBuffer->unlockAsync(fence);
 }
 
 int AHardwareBuffer_sendHandleToUnixSocket(const AHardwareBuffer* buffer, int socketFd) {