SDL: Treat empty SDL_VIDEODRIVER var to check all video drivers.

SDL Commits
#1 
From 9fae8f7088efab699fcec3e8086db5f40c899314 Mon Sep 17 00:00:00 2001
From: Lee Salzman <[EMAIL REDACTED]>
Date: Sun, 29 Aug 2021 15:33:58 -0400
Subject: [PATCH] Treat empty SDL_VIDEODRIVER var to check all video drivers.

---
 src/video/SDL_video.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/video/SDL_video.c b/src/video/SDL_video.c
index 160190da9d..07c7aa5eac 100644
--- a/src/video/SDL_video.c
+++ b/src/video/SDL_video.c
@@ -489,7 +489,7 @@ SDL_VideoInit(const char *driver_name)
     if (driver_name == NULL) {
         driver_name = SDL_getenv("SDL_VIDEODRIVER");
     }
-    if (driver_name != NULL) {
+    if (driver_name != NULL && *driver_name != 0) {
         const char *driver_attempt = driver_name;
         while(driver_attempt != NULL && *driver_attempt != 0 && video == NULL) {
             const char* driver_attempt_end = SDL_strchr(driver_attempt, ',');