Avoid calling malloc() or calloc() with 0 byte.

Submitted by: jtytgat
Ticket:	      #434

git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2972 95820547-d848-0410-985e-9ae8fe0fa350
Do not dereference a NULL pointer in dwarf_add_line_entry() when
dwarf_lne_set_address() hasn't actually been called before.

Submitted by: jtytgat
Ticket:	      #435

git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2973 95820547-d848-0410-985e-9ae8fe0fa350
Deal with unmatched DW_MACINFO_start_file/DW_MACINFO_end_file pairs
and avoid accessing file index out-of-bounds.

Submitted by: jtytgat
Ticket:	      #436

git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2974 95820547-d848-0410-985e-9ae8fe0fa350