player: fix rewind
changed: Have CurlFile return m_bufferSize as chunksize
fixed: FileCache-full logic was wrong + create seperate IsCacheFull() functions
fixed: Don't keep reading source when cache is full (fixes #15500)
changed: Show cachebytes from input in dvdplayer info as it's more intuitive
AE: always request float from sink when in fixed mode, fixes unwanted re-init of sink