Fix SEGV when fhdr.num_nodes == 0 by moving the zeroing of node_vec within the guard.
Fix SEGV when fhdr.num_nodes == 0 by moving the zeroing of node_vec within the guard.

zcth428/hpctoolkit111,zcth428/hpctoolkit111,HPCToolkit/hpctoolkit,zcth428/hpctoolkit,zcth428/hpctoolkit,zcth428/hpctoolkit,zcth428/hpctoolkit111,HPCToolkit/hpctoolkit,zcth428/hpctoolkit,zcth428/hpctoolkit111,HPCToolkit/hpctoolkit,zcth428/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,zcth428/hpctoolkit111,HPCToolkit/hpctoolkit