stream: always disable cache for pseudo-streams

Streams which don't have a full_buffer function never return any actual
data. Slight improvement over commit 5640c195.

stream/stream.c

@@ -325,6 +325,9 @@ static int open_internal(const stream_info_t *sinfo, struct stream *underlying,
     if (!s->read_chunk)
         s->read_chunk = 4 * (s->sector_size ? s->sector_size : STREAM_BUFFER_SIZE);
 
+    if (!s->fill_buffer)
+        s->allow_caching = false;
+
     assert(s->seekable == !!s->seek);
 
     s->uncached_type = s->type;

stream/stream_edl.c

@@ -7,7 +7,6 @@ static int s_open (struct stream *stream)
 {
     stream->type = STREAMTYPE_EDL;
     stream->demuxer = "edl";
-    stream->allow_caching = false;
 
     return STREAM_OK;
 }