[SDL] Segfault in latest mouse scale changes

[M. Gerhardy]

Looks like the hint is not checked for null properly

Here is the stacktrace:
#0 __GI_____strtod_l_internal (nptr=0x0, endptr=0x0, group=<optimized
out>, loc=0x7ffff4f4b400 <_nl_global_locale>) at strtod_l.c:583
#1 0x0000000000667a55 in SDL_atof_REAL (string=0x0) at
/home/mgerhardy/dev/engine/contrib/libs/sdl2/src/stdlib/SDL_string.c:775
#2 0x00000000006470b9 in SDL_MouseNormalSpeedScaleChanged
(userdata=0xa431c0 <SDL_mouse>, name=0x7554bd
"SDL_MOUSE_NORMAL_SPEED_SCALE", oldValue=0x0, hint=0x0)
at
/home/mgerhardy/dev/engine/contrib/libs/sdl2/src/events/SDL_mouse.c:48
#3 0x0000000000699729 in SDL_AddHintCallback_REAL (name=0x7554bd
"SDL_MOUSE_NORMAL_SPEED_SCALE", callback=0x647090
<SDL_MouseNormalSpeedScaleChanged>,
userdata=0xa431c0 <SDL_mouse>) at
/home/mgerhardy/dev/engine/contrib/libs/sdl2/src/SDL_hints.c:187
#4 0x0000000000647041 in SDL_MouseInit () at
/home/mgerhardy/dev/engine/contrib/libs/sdl2/src/events/SDL_mouse.c:65
#5 0x0000000000674e4b in SDL_VideoInit_REAL (driver_name=0x0) at
/home/mgerhardy/dev/engine/contrib/libs/sdl2/src/video/SDL_video.c:474
#6 0x00000000006972d1 in SDL_InitSubSystem_REAL (flags=16416) at
/home/mgerhardy/dev/engine/contrib/libs/sdl2/src/SDL.c:170
#7 0x0000000000697613 in SDL_Init_REAL (flags=32) at
/home/mgerhardy/dev/engine/contrib/libs/sdl2/src/SDL.c:241
#8 0x000000000062d608 in SDL_Init (a=32) at
/home/mgerhardy/dev/engine/contrib/libs/sdl2/src/dynapi/SDL_dynapi_procs.h:89

Regards
Martin