If tf.handle() fails, it returns -1; we shouldn't call ws_fdopen() on
its return value.  (I'm not sure whether it can fail, but this code is
all a bit twisty.)

If tf.handle() succeeds, and we hand its return value to ws_fdopen(),
and we get back NULL, *that* indicates that ws_fdopen() failed.

This should fix Coverity CID 1457929, preventing a FILE leak.

Change-Id: I23bb04579d26928037f8b9284b7741affc3596f7
Reviewed-on: https://code.wireshark.org/review/35940


Petri-Dish: Guy Harris <guy@alum.mit.edu>
Tested-by: Petri Dish Buildbot
Reviewed-by: Guy Harris <guy@alum.mit.edu>