mem: add logic check for static analyzer

mem: add logic check for static analyzer

Technically, single file segments codepath will never get
triggered when using in-memory mode, because EAL prohibits
mixing these two options at initialization time. However,
code analyzers do not know that, and some will complain
about either using uninitialized variables, or trying to
do operations on an already closed descriptor.

Fix this by assuring the compiler or code analyzer that
in-memory mode code never gets triggered when using
single-file segments mode.

Coverity issue: 302847
Fixes: 72b49ff623c4 ("mem: support --in-memory mode")

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>