fix: allow reporting domains when there are none specified

This previously bailed if the response was empty, which in this case is incorrect, as the response isn't based on whether the app is deployed or not.

tests/unit/20_domains.bats

@@ -173,6 +173,11 @@ teardown() {
   echo "status: $status"
   assert_success
 
+  run /bin/bash -c "dokku domains:report $TEST_APP"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
   run /bin/bash -c "dokku domains:clear $TEST_APP"
   echo "output: $output"
   echo "status: $status"
@@ -183,6 +188,11 @@ teardown() {
   echo "status: $status"
   assert_success
   refute_line test.app.dokku.me
+
+  run /bin/bash -c "dokku domains:report $TEST_APP"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
 }
 
 @test "(domains) domains:add-global" {