Fix potential map::at error

There are some potential errors, when using the map::at method,
the process may hang due to out of bounds. so the exception should
be caught.

Also, use the map::contains method of C++20 instead of map::find.

Tested: built pldm successfully and worked.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: Ia5d7dea906e5c598072c08b27387195ef1201839