SDL_mixer: add "gdm" among the module music extensions after the libmodplug update

SDL Commits
1 
From 39d7c2bfe86d0589469b50b0e67287c0169a41fd Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Sun, 20 Jun 2021 03:01:04 +0300
Subject: [PATCH] add "gdm" among the module music extensions after the
 libmodplug update

---
 src/music.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/music.c b/src/music.c
index 8e75d8f..711f8ba 100644
--- a/src/music.c
+++ b/src/music.c
@@ -611,6 +611,7 @@ Mix_Music *Mix_LoadMUS(const char *file)
                     SDL_strcasecmp(ext, "DBM") == 0 ||
                     SDL_strcasecmp(ext, "DSM") == 0 ||
                     SDL_strcasecmp(ext, "FAR") == 0 ||
+                    SDL_strcasecmp(ext, "GDM") == 0 ||
                     SDL_strcasecmp(ext, "IT") == 0 ||
                     SDL_strcasecmp(ext, "MED") == 0 ||
                     SDL_strcasecmp(ext, "MDL") == 0 ||