runtime: fix off-by-one error finding module for PC
Also fix compiler-invoked panics to avoid a confusing "malloc deadlock"
crash if they are invoked while executing the runtime.
Fixes #14599.
Change-Id: I89436abcbf3587901909abbdca1973301654a76e
Reviewed-on: https://go-review.googlesource.com/20219
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-on: https://go-review.googlesource.com/22042 Reviewed-by: Ian Lance Taylor <iant@golang.org>