cmd/go/internal/module: in VersionError, do not wrap an existing ModuleError
VersionError wraps the given error in a ModuleError struct.
If the given error is already a ModuleError for the same path and
version, we now return it directly instead of wrapping.
This makes it safer to call VersionError if we don't know whether
a given error is already wrapped.
Updates #30748
Change-Id: I41b23f6c3ead0ec382e848696da51f478da1ad35
Reviewed-on: https://go-review.googlesource.com/c/go/+/189781
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Jay Conrod <jayconrod@google.com>