pdbdump: fix bug in name hash table.

name_ids() did not return all IDs but only the first NameCount items.
The number of non-zero entries in IDs vector is NameCount, but it
does not mean that all non-zero entries are at the beginning of IDs
vector.

Differential Revision: http://reviews.llvm.org/D20611

llvm-svn: 270656