Report memory snapshot only when read info successfully from procfs

Although rare, there is a chance reading memory snapshot from procfs
could fail due to not able to open/parse file `/proc/self/status` in
`ProcfsMemoryUtil.readMemorySnapshotFromProcefs()`.

This CL checks the result and only report post-gc memory snapshot
when the result is valid.

Bug: 443751950
Flag: EXEMPT bugfix
Change-Id: I42a6fdea8e8765d5490770daf90510064632fb1d