setup: recent version of SDL2_mixer don't have smpeg2

On the 2.0.5 version, there is no smpeg2 anymore. The current dmg on their website have:

08:42 tito@kpax ~  $ otool -L /Volumes/SDL2_mixer/SDL2_mixer.framework/Frameworks/*.framework/Versions/A/{Opus,OpusFile,Vorbis,mpg123,Ogg,FLAC}|grep SDL2
/Volumes/SDL2_mixer/SDL2_mixer.framework/Frameworks/Opus.framework/Versions/A/Opus:
/Volumes/SDL2_mixer/SDL2_mixer.framework/Frameworks/OpusFile.framework/Versions/A/OpusFile:
/Volumes/SDL2_mixer/SDL2_mixer.framework/Frameworks/Vorbis.framework/Versions/A/Vorbis:
/Volumes/SDL2_mixer/SDL2_mixer.framework/Frameworks/mpg123.framework/Versions/A/mpg123:
/Volumes/SDL2_mixer/SDL2_mixer.framework/Frameworks/Ogg.framework/Versions/A/Ogg:
/Volumes/SDL2_mixer/SDL2_mixer.framework/Frameworks/FLAC.framework/Versions/A/FLAC:

No fix needed at all as all the framework doesn't have an rpath to SDL2_mixer
framework.

setup.py

@@ -367,12 +367,17 @@ def update_if_changed(self, fn, content):
 
 
 def _check_and_fix_sdl2_mixer(f_path):
+    # Between SDL_mixer 2.0.1 and 2.0.4, the included frameworks changed
+    # smpeg2 have been replaced with mpg123, but there is no need to fix.
+    smpeg2_path = ("{}/Versions/A/Frameworks/smpeg2.framework"
+                   "/Versions/A/smpeg2").format(f_path)
+    if not exists(smpeg2_path):
+        return
+
     print("Check if SDL2_mixer smpeg2 have an @executable_path")
     rpath_from = ("@executable_path/../Frameworks/SDL2.framework"
                   "/Versions/A/SDL2")
     rpath_to = "@rpath/../../../../SDL2.framework/Versions/A/SDL2"
-    smpeg2_path = ("{}/Versions/A/Frameworks/smpeg2.framework"
-                   "/Versions/A/smpeg2").format(f_path)
     output = getoutput(("otool -L '{}'").format(smpeg2_path)).decode('utf-8')
     if "@executable_path" not in output:
         return