plex: implement 'isDownloadable' flag

(cherry picked from commit d3228d236dfe97cbbbac17f603aee4a11adc5330)
Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>

SharedSources/ServerBrowsing/Plex/VLCNetworkServerBrowserPlex.h

@@ -30,6 +30,7 @@ NS_ASSUME_NONNULL_BEGIN
 @property (nonatomic, readonly, nullable) NSString *duration;
 @property (nonatomic, readonly, nullable) NSURL *subtitleURL;
 @property (nonatomic, readonly, nullable) NSURL *thumbnailURL;
+@property (nonatomic, getter=isDownloadable, readonly) BOOL downloadable;
 
 @end
 

SharedSources/ServerBrowsing/Plex/VLCNetworkServerBrowserPlex.m

@@ -202,6 +202,12 @@
     return self;
 }
 
+- (BOOL)isDownloadable
+{
+    //VLC also needs an extension in the filename for this to work.
+    return YES;
+}
+
 - (VLCMedia *)media
 {
     if (!_URL)