Allow HANDLER PREV and NEXT also after positioning the cursor with a unique search on the primary key


innobase/include/row0mysql.h:
  Allow HANDLER PREV and NEXT also after positioning the cursor with a unique search on the primary key
innobase/row/row0mysql.c:
  Allow HANDLER PREV and NEXT also after positioning the cursor with a unique search on the primary key
innobase/row/row0sel.c:
  Allow HANDLER PREV and NEXT also after positioning the cursor with a unique search on the primary key
sql/ha_innodb.cc:
  Allow HANDLER PREV and NEXT also after positioning the cursor with a unique search on the primary key