Address FindBugs warnings

This commit fixes 36 of the 109 warnings.
Check file size after download

This commit may address symptoms seen in #187 and #197 where
AntennaPod did not flag incomplete downloads as failed.
Merge branch 'http-downloader-check-size' of git://github.com/andrewgaul/AntennaPod into andrewgaul-http-downloader-check-size

Conflicts:
	src/de/danoeh/antennapod/service/download/HttpDownloader.java
PlaybackService crashed when media file was incorrect/not found
Catch ActivityNotFoundException to prevent crash.

This problem occurred with some podcasts using embedded youtube videos. In these cases, the 'http:"-part of the URL was missing and therefore, no activity for viewing the URL was found.
Merge branch 'findbugs' of git://github.com/andrewgaul/AntennaPod into andrewgaul-findbugs

Conflicts:
	src/de/danoeh/antennapod/activity/DownloadActivity.java
	src/de/danoeh/antennapod/asynctask/OpmlExportWorker.java
	src/de/danoeh/antennapod/feed/Feed.java
	src/de/danoeh/antennapod/feed/FeedItem.java
	src/de/danoeh/antennapod/feed/FeedMedia.java
	src/de/danoeh/antennapod/service/download/DownloadStatus.java
	src/de/danoeh/antennapod/storage/DownloadRequester.java
	src/de/danoeh/antennapod/storage/PodDBAdapter.java