smb: fix file reopening issue

smb: fix file reopening issue

Fuzzing highlighted an issue where a command sequence on the same file
id triggered a logging issue:

file data for id N
close id N
file data for id N

If this happened in a single blob of data passed to the parser, the
existing file tx would be reused, the file "reopened", confusing the
file logging logic. This would trigger a debug assert.

This patch makes sure a new file tx is created for the file data
coming in after the first file tx is closed.

Bug: #5567.