dwarf-reader: Create new corpus unconditionally

dwarf-reader: Create new corpus unconditionally

The DWARF reader appears to create a new corpus object only if one is
not already present. However, the only case where there can be
multiple corpora is when build_corpus_group_from_kernel_dist_under is
called and this function clears down the reader context, including the
current corpus, between reading ELF objects.

So it's clearer to just create a fresh corpus object unconditionally
in the DWARF reader.

	* src/abg-dwarf-reader.cc (read_debug_info_into_corpus):
	Create new corpus object unconditionally.

Signed-off-by: Giuliano Procida <gprocida@google.com>
Signed-off-by: Dodji Seketeli <dodji@redhat.com>