fix: Update account limit selection logic (#6149)

spec/enterprise/models/account_spec.rb

@@ -38,5 +38,27 @@ RSpec.describe Account do
         }
       )
     end
+
+    it 'returns max limits from global config if account limit is absent' do
+      account.update(limits: { agents: '' })
+      expect(account.usage_limits).to eq(
+        {
+          agents: 20,
+          inboxes: ChatwootApp.max_limit
+        }
+      )
+    end
+
+    it 'returns max limits from app limit if account limit and installation config is absent' do
+      account.update(limits: { agents: '' })
+      InstallationConfig.where(name: 'ACCOUNT_AGENTS_LIMIT').update(value: '')
+
+      expect(account.usage_limits).to eq(
+        {
+          agents: ChatwootApp.max_limit,
+          inboxes: ChatwootApp.max_limit
+        }
+      )
+    end
   end
 end