fix memory leaks on ClipboardUtil::clipboard_text() and filesystem::base_path()

[kyren]

Namely SDL_GetBasePath and SDL_GetClipboardText.

For stupid reasons, we have to call SDL_GetClipboardText every frame, and we discovered a pretty bad memory leak if you HAPPENED to have large clipboard content.

There may be other errors of the same pattern, but I haven't looked for them.

[Cobrand]

Funny how this went unnoticed for years while this is the very first line of the SDL2 documentation:

Use this function to get UTF-8 text from the clipboard, which must be freed with SDL_free()

Looks like the memory leaks happen anyway but they just get noticeable when you call this function hundreds of time and with large clipboard contents. Thanks for the PR, appreciate it! Will definitely need to check every call that returns text somehow in the future...