Handle invalid profiles gracefully

[kolesnikovae]

Ingestion handling of pprof is currently quite unsafe, meaning that a panic is possible on any unexpected profile structure. For example, elements with ID 0 (not allowed in pprof) may cause panic like this:

Instead, only affected elements should be discarded from the profile, and the valid part should be preserved.

[kolesnikovae]

Note that this specific case is an exclusion: a location may have mapping ID 0