FIX: status was clearing after editing user preferences (#18887)

The problem was reported as a problem with changing theme in user preferences, after saving a new theme the previously set user status was disappearing (https://meta.discourse.org/t/user-status/240335/42). Turned out though that the problem was more wide, changing pretty much any setting in user preferences apart from user status itself led to clearing the status.

spec/requests/users_controller_spec.rb

@@ -2578,6 +2578,25 @@ RSpec.describe UsersController do
           expect(user1.user_status).not_to be_nil
         end
 
+        it "doesn't clear user status if it wasn't sent in the payload" do
+          new_status = {
+            emoji: "off to dentist",
+            description: "tooth",
+          }
+          user.set_status!(new_status[:description], new_status[:emoji])
+          user.reload
+
+          put "/u/#{user.username}.json", params: {
+            bio_raw: "new bio"
+          }
+          expect(response.status).to eq(200)
+
+          user.reload
+          expect(user.user_status).not_to be_nil
+          expect(user.user_status.emoji).to eq(new_status[:emoji])
+          expect(user.user_status.description).to eq(new_status[:description])
+        end
+
         context 'when user status is disabled' do
           before do
             SiteSetting.enable_user_status = false