decoder/modplug: check InputStream::KnownSize()

src/decoder/plugins/ModplugDecoderPlugin.cxx

@@ -54,7 +54,15 @@ modplug_decoder_init(const config_param &param)
 static WritableBuffer<uint8_t>
 mod_loadfile(Decoder *decoder, InputStream &is)
 {
-	const InputStream::offset_type size = is.GetSize();
+	//known/unknown size, preallocate array, lets read in chunks
+
+	const bool is_stream = !is.KnownSize();
+
+	WritableBuffer<uint8_t> buffer;
+	if (is_stream)
+		buffer.size = MODPLUG_PREALLOC_BLOCK;
+	else {
+		const auto size = is.GetSize();
 
 		if (size == 0) {
 			LogWarning(modplug_domain, "file is empty");
@@ -66,12 +74,9 @@ mod_loadfile(Decoder *decoder, InputStream &is)
 			return { nullptr, 0 };
 		}
 
-	//known/unknown size, preallocate array, lets read in chunks
-
-	const bool is_stream = size < 0;
+		buffer.size = size;
+	}
 
-	WritableBuffer<uint8_t> buffer;
-	buffer.size = is_stream ? MODPLUG_PREALLOC_BLOCK : size;
 	buffer.data = new uint8_t[buffer.size];
 
 	uint8_t *const end = buffer.end();