Fix handleLinkNeighbors return value

handleLinkNeighbors returned the next node even if no siblings were consumed
for the tail, which caused further processing (unpackDOMFragments currently)
to be skipped for this node.

This broke parsing for

"[[Foo|<math>bar</math>]] [[Bar]]"

This patch makes sure that handleLinkNeighbours only returns the next node to
process if tail nodes were actually consumed. This fixes semantic errors on
en:Richter's_scale without adding an additional DOM pass as implemented in
alternative patch I369de325b79c85317a95869ddc10e1a0884b1ef6.

Change-Id: I8575676fef28a99435745378b62ef0a64f55210b