Improved STORE_MEM_CLIENT detection.

Improved STORE_MEM_CLIENT detection.

IN_MEMORY mem_status does not guarantee that the entore object is in the
memory cache. We may be just loading it from a shared memrory cache, and
loading may fail. We may have nibbled at the entry already (although that may
not be possible, not sure). The whole memory/disk store_client designation
probably needs more work, but the now-removed condition was causing
store_client.cc:445: "STORE_DISK_CLIENT == getType()" assertions.