Update HttpCacheRequestHandlerAsync.cs

there were cases where webexception catch block was not setting an error. Default the error.
Update CacheControllerAsync.cs

 // When there are records records that are not uploading successfully a successfull download 1-N records will cause anchor to be updated if anchor is updated then the records on the device will not be attempted for upload again on subsequent syncs. therefore check for null Error
Update HttpCacheRequestHandlerAsync.cs

default the error when webexception occurs. see comments inline
Merge branch 'master' of https://github.com/nickharris/syncwinrt
Merge branch 'patch-1' of https://github.com/nickharris/SyncWinRT