osd/PGLog.h: update missing set verification for deletes

osd/PGLog.h: update missing set verification for deletes

Deleted objects may still be on-disk after merging a log that includes
deletes, so adjust the asserts accordingly.

A case like:

980'1192 (972'1186) modify foo
--- osd restart ---
999'1196 (980'1192) delete foo
1003'1199 (0'0) modify foo
1015'1208 (1003'1199) delete foo

Would trigger the assert(miter->second.have == oi.info) since the
'have' version would would be reset to 0'0.

Signed-off-by: Josh Durgin <jdurgin@redhat.com>