[SDL2] pointer boolean (#8523)

src/misc/SDL_url.c

@@ -23,7 +23,7 @@
 
 int SDL_OpenURL(const char *url)
 {
-    if (url == NULL) {
+    if (!url) {
         return SDL_InvalidParamError("url");
     }
     return SDL_SYS_OpenURL(url);

src/misc/windows/SDL_sysurl.c

@@ -44,7 +44,7 @@ int SDL_SYS_OpenURL(const char *url)
     }
 
     wurl = WIN_UTF8ToStringW(url);
-    if (wurl == NULL) {
+    if (!wurl) {
         WIN_CoUninitialize();
         return SDL_OutOfMemory();
     }