Loading indicators aren't show when switching between landing pages

Sorry I didn’t catch this when doing local testing, I must not have noticed as I was on a fast enough connection that blinking would hide the fact that no loading bars appeared.

Describe the problem and steps to reproduce it:

If you are on a landing page (/extensions/ or /themes/) then navigate to the other landing page, loading indicators are not shown and the old content remains until the new content is loaded from the server.

What happened?

The old content remains until the new content loads.

What did you expect to happen?

There to be an intermediate loading state while the route changes but the load is taking place.

Screencasts

Loading animation happens on first landing page load, but not on subsequent loads:

[kumar303]

Yeah, the loading attribute controls the loading indicators (the blurry lines) but also the presence of each set of add-ons, i.e. state.featured. I think the thing to do is reset each set of add-ons when a new request gets started. For example:

diff --git a/src/amo/reducers/landing.js b/src/amo/reducers/landing.js
index 6c159823..7fa7272b 100644
--- a/src/amo/reducers/landing.js
+++ b/src/amo/reducers/landing.js
@@ -18,7 +18,7 @@ export default function landing(state = initialState, action) {
   switch (action.type) {
     case LANDING_GET:
       return {
-        ...state,
+        ...initialState,
         addonType: payload.addonType,
         loading: true,
         resultsLoaded: false,

[ValentinaPC]

Verified this on AMO-dev FF54(Win 7). Loading indicators are shown almost everywhere. While loading Extensions homepage coming from Explore the indicators are not shown. Things seem to work as expected while coming back from Themes. Is this ok, @muffinresearch ? Please see video: