debuggerd_fallback: fix fd leak.

Previously, when we received simultaneous dump requests, we were CASing
a file descriptor value into a variable, and then failing to close it
if the CAS failed.

Bug: http://b/118412443
Test: debuggerd_test
Change-Id: I075c35a239426002eb9416da3d268c3d1a18e9d2
1 file changed