Fix crash on progress pull: gotoPercent is not a document method

Pulling progress crashed KOReader in syncToProgress when the target
wasn't a page number or xpointer (e.g. an epubcfi string from the
server on a rolling document, falling to the percentage branch):
'attempt to call method gotoPercent (a nil value)'. Documents have no
such method — navigation goes through events, exactly as the other
branches in this function already do.

The percentage fallback now dispatches Event GotoPercent (0-100),
handled by ReaderRolling:onGotoPercent and ReaderPaging:onGotoPercent
(the built-in Go-to-% handlers, which also refresh the view). The
redundant UpdatePos follow-up is gone; handlers do it.

Verified all four paths in the stub harness: rolling+percentage →
Event:GotoPercent, rolling+xpointer → Event:GotoXPointer, paging+
page → Event:GotoPage, paging+unresolvable → no-op. No crashes.

main.lua

@@ -909,8 +909,11 @@ function Bookhoard:syncToProgress(progress, percentage)
     elseif progress and progress:match("^/body/") then
         self.ui:handleEvent(Event:new("GotoXPointer", progress))
     elseif percentage then
-        self.ui.document:gotoPercent(percentage * 100)
+        -- Navigation goes through events (ReaderRolling/ReaderPaging both
-        self.ui:handleEvent(Event:new("UpdatePos"))
+        -- implement onGotoPercent and refresh the view themselves). Calling
+        -- document:gotoPercent directly crashed KOReader — no such method
+        -- exists on documents.
+        self.ui:handleEvent(Event:new("GotoPercent", percentage * 100))
     end
 end