haptic: Fix initial detection of haptic devices on Linux system

SDL_UDEV_Scan must be called during SDL_SYS_HapticInit to ensure devices
outside of the 0-31 range are added to the list of haptic devices.

Fixes Bugzilla #3923.

--HG--
extra : histedit_source : 3244924c52322015bb86e5aa1168270ac457f7f7

src/haptic/linux/SDL_syshaptic.c

@@ -181,6 +181,9 @@ SDL_SYS_HapticInit(void)
         SDL_UDEV_Quit();
         return SDL_SetError("Could not setup haptic <-> udev callback");
     }
+
+    /* Force a scan to build the initial device list */
+    SDL_UDEV_Scan();
 #endif /* SDL_USE_LIBUDEV */
 
     return numhaptics;