Update dr_mp3 to 0.6.34.

Closes #1898

license.txt

@@ -99,7 +99,7 @@ This distribution contains code from the following projects (full license text b
 
  - dr_mp3
 	Website: https://mackron.github.io/dr_libs/
-	Source download: https://github.com/mackron/dr_libs/blob/47fdc9d/dr_mp3.h
+	Source download: https://github.com/mackron/dr_libs/blob/dd762b8/dr_mp3.h
 	License: MIT/Expat
 	Copyright 2018 David Reid
 

src/modules/sound/lullaby/MP3Decoder.cpp

@@ -144,7 +144,7 @@ MP3Decoder::MP3Decoder(Stream *stream, int bufferSize)
 		throw love::Exception("Could not find first valid mp3 header.");
 
 	// initialize mp3 handle
-	if (!drmp3_init(&mp3, onRead, onSeek, this, nullptr, nullptr))
+	if (!drmp3_init(&mp3, onRead, onSeek, this, nullptr))
 		throw love::Exception("Could not read mp3 data.");
 
 	sampleRate = mp3.sampleRate;