A random assortment of fixes (#9513)

* Android: Make sure sdcv can find the STL
* DocCache: Be less greedy when serializing to disk, and only do that for the *current* document ;).
* CanvasContext: Explicitly document API quirks.
* Fontlist: Switch the on-disk Persist format to zstd (it's ever so slightly faster).
* Bump base for https://github.com/koreader/koreader-base/pull/1515 (fix #9506)

frontend/apps/reader/readerui.lua

@@ -761,9 +761,9 @@ function ReaderUI:onClose(full_refresh)
     if self.dialog ~= self then
         self:saveSettings()
     end
-    -- Serialize the most recently displayed page for later launch
-    DocCache:serialize()
     if self.document ~= nil then
+        -- Serialize the most recently displayed page for later launch
+        DocCache:serialize(self.document.file)
         logger.dbg("closing document")
         self:notifyCloseDocument()
     end