Fix a race conditon provoking the error no such file '/pve-storage-content'

Fix a race conditon provoking the error no such file '/pve-storage-content'

(NB: the error was only displayed intermittently in the browser console)

The reload call could try a store reload before the store has
a defined url.
The call here is useless since the initial display of
the storage selector compoment will call setStorage() to pass an url
to the store and load it.

Also remove the test on me.store.proxy.url since it was not working
(ExtJS autodefined an URL based on the model name)