hdf5_ep

Fix HDFFV-10274.  When deleting all (or almost all) of the messages in
an object header chunk, where the total amount deleted was greater than
64K, an error would occur due to an off by one error in the code that
handled that case.  Fixed this and added a test case.
(cherry picked from commit 1b2c2ca9a6a7d7e1fcd5c3302e203f2e2dabf0af)