Don't return true from DoTryChain() if the event wasn't really processed.

Don't return true from DoTryChain() if the event wasn't really processed.

Correct the return value when an event handler didn't honour "process only in
this handler" flag: we shouldn't pass the event to the further handlers in
this case but we shouldn't return true neither as the event wasn't really
processed.

This corrects background painting of wxHtmlWindow broken by previous changes.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64495 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775