Fixed crash when tablet isn't detected properly

src/events/SDL_mouse.c

@@ -374,6 +374,11 @@ SDL_SendProximity(int id, int x, int y, int type)
     int index = SDL_GetMouseIndexId(id);
     SDL_Mouse *mouse = SDL_GetMouse(index);
     int posted = 0;
+
+    if (!mouse) {
+        return 0;
+    }
+
     last_x = x;
     last_y = y;
     if (SDL_ProcessEvents[type] == SDL_ENABLE) {

src/events/SDL_mouse_c.h

@@ -112,15 +112,18 @@ extern void SDL_ResetMouse(int index);
 /* Set the mouse focus window */
 extern void SDL_SetMouseFocus(int id, SDL_WindowID windowID);
 
-/* Send a mouse motion event for a mouse at an index */
+/* Send a mouse motion event for a mouse */
 extern int SDL_SendMouseMotion(int id, int relative, int x, int y, int z);
 
-/* Send a mouse button event for a mouse at an index */
+/* Send a mouse button event for a mouse */
 extern int SDL_SendMouseButton(int id, Uint8 state, Uint8 button);
 
-/* Send a mouse wheel event for a mouse at an index */
+/* Send a mouse wheel event for a mouse */
 extern int SDL_SendMouseWheel(int id, int x, int y);
 
+/* Send a proximity event for a mouse */
+extern int SDL_SendProximity(int id, int x, int y, int type);
+
 /* Shutdown the mouse subsystem */
 extern void SDL_MouseQuit(void);