[geary/wip/181-special-folder-dupes] Fix ambiguous test in AccountInformation.set_special_folder

[Michael Gratton <mjog src gnome org>]

commit c0faf9ed65b507ee6ab1c74c4344857c5af5cc3d
Author: Michael Gratton <mike vee net>
Date:   Mon Jan 14 18:05:20 2019 +1100

    Fix ambiguous test in AccountInformation.set_special_folder

 src/engine/api/geary-account-information.vala | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/src/engine/api/geary-account-information.vala b/src/engine/api/geary-account-information.vala
index edc867a1..35b4a5fd 100644
--- a/src/engine/api/geary-account-information.vala
+++ b/src/engine/api/geary-account-information.vala
@@ -437,8 +437,9 @@ public class Geary.AccountInformation : BaseObject {
             break;
         }
 
-        if (old_path == null && new_path != null ||
-            old_path != null && !old_path.equal_to(new_path)) {
+        if ((old_path == null && new_path != null) ||
+            (old_path != null && new_path == null) ||
+            (old_path != null && !old_path.equal_to(new_path))) {
             changed();
         }
     }