Only free undequeued buffers during Surface::disconnect()

... to prevent Surface from destroying dequeued buffers that have
not yet had a chance to be `ANativeWindow_cancelBuffer()`-ed. See
b/432531444#comment11 for more info.

Bug: b/432531444
Test: cvd create --gpu_mode=gfxstream
Test: atest android.uirendering.cts.testclasses.SurfaceViewTests
Flag: EXEMPT bug fix for ag/33785470
Change-Id: I11df4226da7a8fc659b291d86f0a06191a7b2977