decoder/dsf: check InputStream::KnownSize()

src/decoder/plugins/DsfDecoderPlugin.cxx

@@ -155,9 +155,11 @@ dsf_read_metadata(Decoder *decoder, InputStream &is,
 	data_size -= sizeof(data_chunk);
 
 	/* data_size cannot be bigger or equal to total file size */
-	const uint64_t size = (uint64_t)is.GetSize();
-	if (data_size >= size)
-		return false;
+	if (is.KnownSize()) {
+		const uint64_t size = (uint64_t)is.GetSize();
+		if (data_size >= size)
+			return false;
+	}
 
 	/* use the sample count from the DSF header as the upper
 	   bound, because some DSF files contain junk at the end of