when switching sheets quickly, zss sometimes throws a javascript error

Steps to Reproduce

1. load attached file with chrome
set network throttling to "Fast 3G" or "Slow 3G"
2. quickly switching among different sheets

Current Result

zss.wpd:16898 Uncaught TypeError: Cannot read property 'getVisibleRange' of undefined
at init.doSelectSheet (zss.wpd:16898)
at init._onSelectSheet (zss.wpd:16868)
at init.<anonymous> (zk.wpd:10729)
at init.fireX (zk.wpd:17440)
at _fireClick (zk.wpd:15179)
at init.doClick_ (zk.wpd:17643)
at init.$supers (zk.wpd:10802)
at init.doClick_ (zk.wpd:23171)
at init.$supers (zk.wpd:10802)

Expected Result

no error

Debug Information

• it's hard to reproduce for it could be asynchronous timing issue.