[release-branch.go1.15] runtime: non-strict InlTreeIndex lookup in expandFinalInlineFrame
    
    This is a follow-up to golang.org/cl/301369, which made the same change
    in Frames.Next. The same logic applies here: a profile stack may have
    been truncated at an invalid PC provided by cgoTraceback.
    expandFinalInlineFrame will then try to lookup the inline tree and
    crash.
    
    The same fix applies as well: upon encountering a bad PC, simply leave
    it as-is and move on.
    
    For #44971
    For #45480
    Fixes #45481
    
    Change-Id: I2823c67a1f3425466b05384cc6d30f5fc8ee6ddc
    Reviewed-on: https://go-review.googlesource.com/c/go/+/309109
    Reviewed-by: Michael Knyszek <mknyszek@google.com>
    Trust: Michael Pratt <mpratt@google.com>
    (cherry picked from commit aad13cbb749d1e6c085ff0556d306de1a2d5d063)
    Reviewed-on: https://go-review.googlesource.com/c/go/+/309550
    Run-TryBot: Michael Pratt <mpratt@google.com>
    Reviewed-by: Cherry Zhang <cherryyz@google.com>
    TryBot-Result: Go Bot <gobot@golang.org>