devapp/owners: remove requirement of non-empty Gerrit email

Some people may not have a Gerrit account (yet, or in general).
Instead of entering a fake email, just remove the requirement
to have a non-empty Gerrit email. It's useful to have an owner
who only has a GitHub account.

The original code in CL 111295 had a len(p.Emails) == 0 check
because it was attempting to access p.Emails[0], but after
CL 192102, it is safe to use p.Gerrit directly.

Change-Id: I737d287f69f8ff7a0377f8e324bf6318d8c18d94
Reviewed-on: https://go-review.googlesource.com/c/build/+/217540
Reviewed-by: Alexander Rakoczy <alex@golang.org>
Run-TryBot: Alexander Rakoczy <alex@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/devapp/owners/table.go b/devapp/owners/table.go
index a2e1c31..8900b10 100644
--- a/devapp/owners/table.go
+++ b/devapp/owners/table.go
@@ -11,10 +11,7 @@
 func gh(githubUsername string) Owner {
 	p := gophers.GetPerson("@" + githubUsername)
 	if p == nil {
-		panic(githubUsername + " not found")
-	}
-	if p.Gerrit == "" {
-		panic("person with GitHub username " + githubUsername + " must have at least one email")
+		panic("person with GitHub username " + githubUsername + " not found")
 	}
 	return Owner{GitHubUsername: githubUsername, GerritEmail: p.Gerrit}
 }