Modifing attachments when viewing only attachments for a page with ?viewer=attachments redirects to the Document#Attachments url instead of the ?viewer=attachments

To reproduce:

• go to a page's attachments view (through the viewer), say xwiki/bin/view/Sandbox/WebHome?viewer=attachments
• upload a new attachment
• now you're on xwiki/bin/view/Sandbox/WebHome#Attachments instead of back on xwiki/bin/view/Sandbox/WebHome?viewer=attachments

This is annoying in the following situations:
1/ when you want to only handle attachments for a page, you're not interested in the content of a page. In this case you might see things that you're not interested in and loose the focus / not find the list of attachments anymore (if you have a big screen and few attachments, the attachments list is all the way at the bottom when it was high up in the top of the page before)
2/ when you have a different skin applied on the wiki and the attachments tab doesn't exist, therefore #Attachments doesn't make sense. In this case, if you need to make more attachments operations, you need to reput ?viewer=attachments manually at the end of the url every time

Same happens for ?viewer=attachmentsinline and it can be equally annoying.