ctf: Fixed leaked file handle when calling CTFTraceReader.update

ctf: Fixed leaked file handle when calling CTFTraceReader.update

If an instance of CTFStreamInputReader already existed in a
CTFTraceReader, it was not getting closed after checking whether or not
it existed. This was causing a test failure on Windows in
CTFTraceGrowingTest.

Change-Id: Ia064d3270882515b32834456771a108970ce8f8e
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/62515
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>