controllermap: use enum to avoid '-Wmaybe-uninitialized'

Emitted by MinGW:

In function 'WatchJoystick',
    inlined from 'SDL_main' at D:/a/SDL/SDL/test/controllermap.c:802:9:
D:/a/SDL/SDL/test/controllermap.c:437:9: warning: 'marker' may be used uninitialized [-Wmaybe-uninitialized]
  437 |         SDL_SetTextureAlphaMod(marker, alpha);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
D:/a/SDL/SDL/test/controllermap.c: In function 'SDL_main':
D:/a/SDL/SDL/test/controllermap.c:355:71: note: 'marker' was declared here
  355 |     SDL_Texture *background_front, *background_back, *button, *axis, *marker;

test/controllermap.c

@@ -28,8 +28,10 @@
 #define SCREEN_WIDTH    512
 #define SCREEN_HEIGHT   320
 
-#define MARKER_BUTTON 1
-#define MARKER_AXIS 2
+enum marker_type {
+    MARKER_BUTTON,
+    MARKER_AXIS,
+};
 
 enum
 {
@@ -48,11 +50,11 @@ enum
 
 #define BINDING_COUNT (SDL_CONTROLLER_BUTTON_MAX + SDL_CONTROLLER_BINDING_AXIS_MAX)
 
-static struct 
+static struct
 {
     int x, y;
     double angle;
-    int marker;
+    enum marker_type marker;
 
 } s_arrBindingDisplay[] = {
     { 387, 167, 0.0, MARKER_BUTTON }, /* SDL_CONTROLLER_BUTTON_A */
@@ -352,7 +354,7 @@ BMergeAxisBindings(int iIndex)
 static void
 WatchJoystick(SDL_Joystick * joystick)
 {
-    SDL_Texture *background_front, *background_back, *button, *axis, *marker;
+    SDL_Texture *background_front, *background_back, *button, *axis, *marker=NULL;
     const char *name = NULL;
     SDL_Event event;
     SDL_Rect dst;
@@ -407,8 +409,6 @@ WatchJoystick(SDL_Joystick * joystick)
             case MARKER_BUTTON:
                 marker = button;
                 break;
-            default:
-                break;
         }
         
         dst.x = s_arrBindingDisplay[iElement].x;