Use the empty string for note names with zero size (without any data).

Use the empty string for note names with zero size (without any data).

ELF notes can have a zero sized name. In which case there is no data at
all (so also no zero terminator). Make sure to use the empty string for
such notes if the code does not otherwise explicitly check n_namesz.

https://sourceware.org/bugzilla/show_bug.cgi?id=21300

Signed-off-by: Mark Wielaard <mark@klomp.org>