ui: tape/ChangerStatus: handle vanishing view during reload

since reload is an async function, the view can be destroyed during
any 'await' point. Subsequent accesses to the view will fail, and we
will land in the catch. Check there if the view is destroyed, and
do not raise an error with the user then

also cancel any outstanding timer on 'deactivate' and 'destroy'

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

www/tape/ChangerStatus.js

@@ -285,12 +285,17 @@ Ext.define('PBS.TapeManagement.ChangerStatus', {
 	    }
 	},
 
-	reload: function() {
+	cancelReload: function() {
 	    let me = this;
 	    if (me.reloadTimeout !== undefined) {
 		clearTimeout(me.reloadTimeout);
 		me.reloadTimeout = undefined;
 	    }
+	},
+
+	reload: function() {
+	    let me = this;
+	    me.cancelReload();
 	    me.reload_full(true);
 	},
 
@@ -398,6 +403,10 @@ Ext.define('PBS.TapeManagement.ChangerStatus', {
 		}
 		Proxmox.Utils.setErrorMask(me.lookup('content'));
 	    } catch (err) {
+		if (!view || view.isDestroyed) {
+		    return;
+		}
+
 		if (!use_cache) {
 		    Proxmox.Utils.setErrorMask(view);
 		}
@@ -470,11 +479,13 @@ Ext.define('PBS.TapeManagement.ChangerStatus', {
 	    }
 
 	    view.title = `${gettext("Changer")}: ${view.changer}`;
+	    me.reload();
 	},
     },
 
     listeners: {
-	activate: 'reload',
+	deactivate: 'cancelReload',
+	destroy: 'cancelReload',
     },
 
     tbar: [