Improved logging

app/src/main/java/eu/faircode/email/Core.java

@@ -2121,7 +2121,14 @@ class Core {
                 " fetched in " + duration + " ms");
 
         if (ifolders.size() == 0) {
-            Log.e(account.host + " no folders listed");
+            List<String> ns = new ArrayList<>();
+            if (personal == null)
+                ns.add("<null>");
+            else
+                for (Folder f : personal)
+                    ns.add(f.getFullName());
+            Log.e(account.host + " no folders listed" +
+                    " namespaces=" + TextUtils.join(",", ns));
             return;
         }