Fix the UAF bug caused by a dead stack variable

The original code attempts to copy data from a location pointed to by a
local variable that has gone out of scope. This CL moves the copy
operation into the scope.

Test: make cts -j123 && cts-tradefed run cts-dev -m \
CtsMediaTestCases --compatibility:module-arg \
CtsMediaTestCases:include-annotation:\
android.platform.test.annotations.RequiresDevice

Bug: 63773604
Change-Id: I980630b6ac30875c2df65664668d4d6b7414f3a7