Fix message comparison throwing type error when comparing maps in some cases

[osa1]

Fixes #1075.

[osa1]

@sigurdm I think this would ideally be published as 5.0.1, but we already have a bunch of commits in master and the current version is 5.1.0. So we'd need to publish from a branch instead of master. WDYT?

[sigurdm]

@sigurdm I think this would ideally be published as 5.0.1, but we already have a bunch of commits in master and the current version is 5.1.0. So we'd need to publish from a branch instead of master. WDYT?

Unless it's urgent, or you plan to wait a long time before publishing 5.1.0 I would not bother with an intermediate 5.0.1.