Fix: Zsync -> Subscribe to book share crashes (#5184)
Fix: Zsync -> Subscribe to book share crashes (#5184)

Patch similar to PR #3086.
Same problem #2638 when tap Subscribe to book share.
"Zsync" -> "Subscribe to book share" crashes koreader if not connected to wifi

After this fix when koreader is offline after "Zsync" -> "Subscribe to book share" we are asked to enable wifi.
pazos/koreader,poire-z/koreader,Frenzie/koreader,mihailim/koreader,Markismus/koreader,Frenzie/koreader,NiLuJe/koreader,NiLuJe/koreader,poire-z/koreader,koreader/koreader,mwoz123/koreader,koreader/koreader,Hzj-jie/koreader