write_data segmentation fault

Dear all,

The simple input script below produces a segmentation fault when writing data.
Judging by the output, the bug is in accessing velocity of the last atom (see below).

Simple bug fix - will be in next patch.

Replace these lines in write_data.cpp

if (nbonds) bonds();
if (nangles) angles();

with these

if (atom->nbonds && nbonds) bonds();
if (atom->nangles && nangles) angles();