simplify if/else with guards

lib/gitlab/gpg/commit.rb

@@ -83,16 +83,16 @@ module Gitlab
       end
 
       def verification_status(gpg_key)
-        if gpg_key && gpg_key.verified_and_belongs_to_email?(@commit.committer_email) && verified_signature.valid?
+        return GpgSignature.verification_statuses[:unknown_key] unless gpg_key
+        return GpgSignature.verification_statuses[:unverified_key] unless gpg_key.verified?
+        return GpgSignature.verification_statuses[:unverified] unless verified_signature.valid?
+
+        if gpg_key.verified_and_belongs_to_email?(@commit.committer_email)
           GpgSignature.verification_statuses[:verified]
-        elsif gpg_key && gpg_key.verified? && verified_signature.valid? && gpg_key.user.all_emails.include?(@commit.committer_email)
+        elsif gpg_key.user.all_emails.include?(@commit.committer_email)
           GpgSignature.verification_statuses[:same_user_different_email]
-        elsif gpg_key && gpg_key.verified? && verified_signature.valid?
-          GpgSignature.verification_statuses[:other_user]
-        elsif gpg_key
-          GpgSignature.verification_statuses[:unverified_key]
         else
-          GpgSignature.verification_statuses[:unknown_key]
+          GpgSignature.verification_statuses[:other_user]
         end
       end