Client should not crash the server

Ideally, a client should not be able to crash the server on any occasion. However, currently there are multiple ways to crash the server with just pw-cli:

• pw-cli d 2 (deletes libpipewire-module-protocol-native)
• pw-cli d $(pw-cli dump short | grep pw-cli | cut -d':' -f1) (deletes the pw-cli client itself)
• pw-cli d 5 twice (deletes libpipewire-module-metadata)