Fixed bug #329

On tracing it turns out to fail from SDL_WM_SetCaption()

On going through the function it looks like the SDL_free() function is called
every alternate time with an invalid pointer that has already been freed.

include/SDL_compat.h

@@ -147,7 +147,7 @@ extern DECLSPEC SDL_Surface *SDLCALL SDL_DisplayFormatAlpha(SDL_Surface *
                                                             surface);
 extern DECLSPEC void SDLCALL SDL_WM_SetCaption(const char *title,
                                                const char *icon);
-extern DECLSPEC void SDLCALL SDL_WM_GetCaption(char **title, char **icon);
+extern DECLSPEC void SDLCALL SDL_WM_GetCaption(const char **title, const char **icon);
 extern DECLSPEC void SDLCALL SDL_WM_SetIcon(SDL_Surface * icon, Uint8 * mask);
 extern DECLSPEC int SDLCALL SDL_WM_IconifyWindow(void);
 extern DECLSPEC int SDLCALL SDL_WM_ToggleFullScreen(SDL_Surface * surface);

src/SDL_compat.c

@@ -692,14 +692,17 @@ SDL_WM_SetCaption(const char *title, const char *icon)
 {
     if (wm_title) {
         SDL_free(wm_title);
-    } else {
+    }
+    if (title) {
         wm_title = SDL_strdup(title);
+    } else {
+        wm_title = NULL;
     }
     SDL_SetWindowTitle(SDL_VideoWindow, wm_title);
 }
 
 void
-SDL_WM_GetCaption(char **title, char **icon)
+SDL_WM_GetCaption(const char **title, const char **icon)
 {
     if (title) {
         *title = wm_title;