COMP: fixed compilation error using llvm's libc++

ifstream's read() method returns a reference, which
can never be NULL yet vtkEnSightGoldBinaryReader was
comparing the result against NULL.  This fails to
compile if using llvm's libc++.  So, instead of
"if (read() == NULL)" it now does "if (!read())"
which does the right thing (I think)
since operator! is overloaded.

Change-Id: I5412da06795982826bb0df5c7dd82e53b1754e5d
Merge topic 'libc++-fixes' into master

cc1e92f9 COMP: fixed compilation error using llvm's libc++