elfcopy: fix PE object section name corruption and crash

Fixed a bug that the PE object section names are generated incorrectly
using the section name table found in the original input ELF object
instead of the intermediate ELF object.

Ticket: #541

Do not try to copy section content from a NULL d_buf when creating
uninitialized data COFF section for PE object.

Ticket: #540

Obtained from: ELF Tool Chain r3507, r3508
MFC after: 1 week