SDL: Fixed double-comma if the crc is first in the mapping

SDL Commits
1 
From 85eb1fa5150447e127d7c0a2baeed962a2a3223f Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Tue, 18 Jul 2023 17:32:46 -0700
Subject: [PATCH] Fixed double-comma if the crc is first in the mapping

---
 src/joystick/SDL_gamepad.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/joystick/SDL_gamepad.c b/src/joystick/SDL_gamepad.c
index 6d26b3982ffa..901c1a4654ef 100644
--- a/src/joystick/SDL_gamepad.c
+++ b/src/joystick/SDL_gamepad.c
@@ -1465,6 +1465,7 @@ static GamepadMapping_t *SDL_PrivateAddMappingForGUID(SDL_JoystickGUID jGUID, co
         /* Make sure the mapping has the CRC */
         char *new_mapping;
         const char *optional_comma;
+        size_t mapping_length;
         char *crc_end = "";
         char *crc_string = SDL_strstr(pchMapping, SDL_GAMEPAD_CRC_FIELD);
         if (crc_string) {
@@ -1478,7 +1479,8 @@ static GamepadMapping_t *SDL_PrivateAddMappingForGUID(SDL_JoystickGUID jGUID, co
         }
 
         /* Make sure there's a comma before the CRC */
-        if (pchMapping[SDL_strlen(pchMapping) - 1] == ',') {
+        mapping_length = SDL_strlen(pchMapping);
+        if (mapping_length == 0 || pchMapping[mapping_length - 1] == ',') {
             optional_comma = "";
         } else {
             optional_comma = ",";