Fix card infinite scrolling on card activities

I imagine blaze-component changed their Mixins API since I written
this code. We need some tests to avoid this kind of regressions when
updating dependencies!

Fixes #420

client/components/cards/cardDetails.js

@@ -8,8 +8,11 @@ BlazeComponent.extendComponent({
   },
 
   calculateNextPeak() {
-    const altitude = this.find('.js-card-details').scrollHeight;
-    this.callFirstWith(this, 'setNextPeak', altitude);
+    const cardElement = this.find('.js-card-details');
+    if (cardElement) {
+      const altitude = cardElement.scrollHeight;
+      this.callFirstWith(this, 'setNextPeak', altitude);
+    }
   },
 
   reachNextPeak() {
@@ -21,6 +24,7 @@ BlazeComponent.extendComponent({
     this.isLoaded = new ReactiveVar(false);
     this.parentComponent().showOverlay.set(true);
     this.parentComponent().mouseHasEnterCardDetails = false;
+    this.calculateNextPeak();
   },
 
   scrollParentContainer() {

client/components/mixins/infiniteScrolling.js

@@ -17,11 +17,6 @@ Mixins.InfiniteScrolling = BlazeComponent.extendComponent({
     this._nextPeak = Infinity;
   },
 
-  // To be overwritten by consumers of this mixin
-  reachNextPeak() {
-
-  },
-
   events() {
     return [{
       scroll(evt) {
@@ -29,7 +24,7 @@ Mixins.InfiniteScrolling = BlazeComponent.extendComponent({
         let altitude = domElement.scrollTop + domElement.offsetHeight;
         altitude += peakAnticipation;
         if (altitude >= this.callFirstWith(null, 'getNextPeak')) {
-          this.callFirstWith(null, 'reachNextPeak');
+          this.mixinParent().callFirstWith(null, 'reachNextPeak');
         }
       },
     }];

client/components/sidebar/sidebar.js

@@ -94,9 +94,7 @@ BlazeComponent.extendComponent({
   },
 
   events() {
-    // XXX Hacky, we need some kind of `super`
-    const mixinEvents = this.getMixin(Mixins.InfiniteScrolling).events();
-    return [...mixinEvents, {
+    return [{
       'click .js-hide-sidebar': this.hide,
       'click .js-toggle-sidebar': this.toggle,
       'click .js-back-home': this.setView,