Prevent crash when there are no media streams

[cewert]

Discovered playing a livetv channel with no media streams

happening on prod now

req              <uninitialized> 
rule             <uninitialized> 
selectedaudiostream <uninitialized> 
deviceprofile    roAssociativeArray refcnt=1 count:17 
params           roAssociativeArray refcnt=1 count:8 
m                roAssociativeArray refcnt=6 count:7 
global           Interface:ifGloba$1 starttimeticks   LongInteger refcnt=2 val:0 (&h0) 
subtitletrackindex Integer val:-1 (&hFFFFFFFF) 
audiotrackindex  Integer val:1 (&h1) 
mediasourceid    String (VT_STR_CONST) val:"" 
id               roString (2.1 was String) refcnt=1 val:"7ed7d0bbc7413b598ce38a19b1fedf5f" 
Local Variables: 
   file/line: pkg:/source/Main.brs(521) 
#0  Function main(args As Dynamic) As Voi$1 file/line: pkg:/source/ShowScenes.brs(881) 
#1  Function createvideoplayergroup(video_id As String) As Dynami$1 file/line: pkg:/source/VideoPlayer.brs(5) 
#2  Function videoplayer(id As String, mediasourceid As Dynamic, audio_stream_idx As Integer, subtitle_idx As Integer, forcetranscoding As Boolean, showintro As Boolean, allowresumedialog As Boolean) As Dynami$1 file/line: pkg:/source/VideoPlayer.brs(180) 
#3  Function addvideocontent(video As Object, mediasourceid As Dynamic, audio_stream_idx As Integer, subtitle_idx As Integer, playbackposition As Integer, forcetranscoding As Boolean, showintro As Boolean, allowresumedialog As Boolean) As Voi$1 file/line: pkg:/source/api/Items.brs(39) 
#4  Function itempostplaybackinfo(id As String, mediasourceid As String, audiotrackindex As Integer, subtitletrackindex As Integer, starttimeticks As LongInteger) As Dynami$1 Backtrace: 
Array operation attempted on variable not DIM'd. (runtime error &he7) in pkg:/source/api/Items.brs(39)