windows: Call GetWindowText() with the correct parameters (thanks, Zebediah!)

GetWindowText() wants you to tell it the size of the buffer--including the
terminating NULL char--but we weren't counting that last char, losing the
last char of the string in the process. This was only seen with the special
case of SDL_CreateWindowFrom() to use an existing native window, not
the usual SDL_CreateWindow() codepath.

Fixes Bugzilla #4696.

src/video/windows/SDL_windowswindow.c

@@ -386,7 +386,7 @@ WIN_CreateWindowFrom(_THIS, SDL_Window * window, const void *data)
     titleLen = GetWindowTextLength(hwnd);
     title = SDL_small_alloc(TCHAR, titleLen + 1, &isstack);
     if (title) {
-        titleLen = GetWindowText(hwnd, title, titleLen);
+        titleLen = GetWindowText(hwnd, title, titleLen + 1);
     } else {
         titleLen = 0;
     }