playlist_Add and playlist_AddExt: return error/success value
playlist_Add and playlist_AddExt: return error/success value

None of the callers actually care about the return value anyway.
When the input item is needed, then playlist_AddInput did and still
does the job.

xkfz007/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc,krichter722/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,xkfz007/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,shyamalschandra/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,shyamalschandra/vlc,shyamalschandra/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,krichter722/vlc,krichter722/vlc,vlc-mirror/vlc-2.1,vlc-mirror/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.1,krichter722/vlc,shyamalschandra/vlc,vlc-mirror/vlc,vlc-mirror/vlc-2.1,shyamalschandra/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,xkfz007/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.1,shyamalschandra/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,krichter722/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,shyamalschandra/vlc,krichter722/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,krichter722/vlc,jomanmuk/vlc-2.1,jomanmuk/vlc-2.1