Video thumbnails are not generated anymore

Hi Gregory and Ken,

Thanks for your attention to this issue. Here are some details on how we reproduce this issue.

We use method:

- (void)loadThumbnail:(NSString *)path ofSize:(NSString *)size intoPath:(NSString *)destinationPath 

of class DBRestClient from official cocoapod Dropbox-iOS-SDK (version 1.3.13). Parameters:

path (self.metadata.path): "/camera uploads/2/2014-04-10 18.51.53.mov"
size: "l" (lowercase L)
destinationPath: ".../tmp/l-2014-04-10 18.51.53.mov" (... is just for short)

And we got this error in callback:

Error Domain=dropbox.com Code=415 "(null)" UserInfo={path=/camera uploads/2/2014-04-10 18.51.53.mov, size=l, root=dropbox, error=permanent failure - this image isn't supported by thumbnailing, destinationPath=.../tmp/l-2014-04-10 18.51.53.mov}

We get this issue for all videos. Image thumbnailing works for us in all cases.

I've just checked and yes — this issues is still 100% reproducable for us.

Thanks!

Sergey