Bugfix. show method must be debounced per instance

Otherwise it gets debounced for multiple instances and certain chat boxes will
then not get shown.

src/converse-core.js

@@ -2252,12 +2252,21 @@
                 return this;
             },
 
-            show: _.debounce(function (focus) {
+            show: function (focus) {
+                if (typeof this.debouncedShow === 'undefined') {
+                    /* We wrap the method in a debouncer and set it on the
+                     * instance, so that we have it debounced per instance.
+                     * Debouncing it on the class-level is too broad.
+                     */
+                    this.debouncedShow = _.debounce(function (focus) {
                         if (this.$el.is(':visible') && this.$el.css('opacity') === "1") {
                             if (focus) { this.focus(); }
                             return this;
                         }
                         this.initDragResize().setDimensions();
+                        // We call trimChats before fading in, to avoid ugly transition
+                        // effects.
+                        converse.chatboxviews.trimChats(this);
                         this.$el.fadeIn(function () {
                             if (converse.connection.connected) {
                                 // Without a connection, we haven't yet initialized
@@ -2270,8 +2279,11 @@
                                 this.focus();
                             }
                         }.bind(this));
+                    }, 250, true);
+                }
+                this.debouncedShow.apply(this, arguments);
                 return this;
-            }, 250, true),
+            },
 
             scrollDownMessageHeight: function ($message) {
                 if (this.$content.is(':visible')) {