Do not pass NULL to memcpy

ReadJoyConControllerType calls WriteSubcommandSync with pbuf=NULL

src/joystick/hidapi/SDL_hidapi_switch.c

@@ -493,7 +493,9 @@ static void ConstructSubcommand(SDL_DriverSwitch_Context *ctx, ESwitchSubcommand
     SDL_memcpy(outPacket->commonData.rumbleData, ctx->m_RumblePacket.rumbleData, sizeof(ctx->m_RumblePacket.rumbleData));
 
     outPacket->ucSubcommandID = ucCommandID;
-    SDL_memcpy(outPacket->rgucSubcommandData, pBuf, ucLen);
+    if (pBuf) {
+        SDL_memcpy(outPacket->rgucSubcommandData, pBuf, ucLen);
+    }
 
     ctx->m_nCommandNumber = (ctx->m_nCommandNumber + 1) & 0xF;
 }