Fixed showing error if cache is empty and there is no internet connection

app/src/main/java/com/sirekanyan/knigopis/repository/CommonRepository.kt

@@ -22,7 +22,7 @@ abstract class CommonRepository<T>(private val networkChecker: NetworkChecker) {
                     .toMaybe()
             )
         } else {
-            findCached().toFlowable()
+            findCached().toSingle().toFlowable()
         }
 
 }