properly block file upload to non-active filelist

Signed-off-by: Robin Appelman <robin@icewind.nl>

apps/files/js/filelist.js

@@ -2742,6 +2742,7 @@
 
 				if (self.$el.hasClass('hidden')) {
 					// do not upload to invisible lists
+					e.preventDefault();
 					return false;
 				}
 
@@ -2753,6 +2754,7 @@
 					&& !self.$el.has(dropTarget).length // dropped inside list
 					&& !dropTarget.is(self.$container) // dropped on main container
 					) {
+					e.preventDefault();
 					return false;
 				}