speedup Library.LibRenderSavedEpubs()

[gamebeaker]

Double render speed of Library.
The more Bytes are saved in chrome.storage.local or the Library the slower the rendering is.
With the reduction from 2 calls of chrome.storage.local.get() to 1 it is double the speed.

[gamebeaker]

Example:
Download the Art Chapter (first Chapter) from this story:
https://www.royalroad.com/fiction/62881/reborn-as-a-demonic-tree
The size is 28,979 KB upload this epub 5 times in the Library -> reload WebToEpub and open Library -> see the slow render time.
Even with the two times speed up there is a delay.