Sdl fixes: proper rendere selection

Should fix #8490 - the -1 in `SDL_CreateRenderer` instructs SDL to chose any renderer that supports the given flags ( https://wiki.libsdl.org/SDL_CreateRenderer ), but the flag SDL_RENDERER_TARGETTEXTURE was not provided. SDL did chose a hardware renderer which did not support rendering to a texture. Therefor `SDL_SetRenderTarget` fails - as shown in the log in that issue.

With the flag, SDL will either choose a hardware renderer that supports this, or fail to select a hardware renderer at all. In the later case the software renderer will be used as fallback (that code already exists), which apparently works fine.

It *might* partially fix the issue #8510 - there are two code paths leading to the messages being printed:
- one at the end of game::draw,
- another through handle_mouseview -> hide_mouseview -> write_msg.

This leads to `wrefresh(w_messages)` being called twice, which I believe caused the flickering. I once experienced this flicked, but was unable to reproduce it now, so this might not have fixed it. Better wait for Wuzzy to confirm (and close the issue) or deny it.

This also fixes the "minimap stays black after closing certain windows" issue. The minimap was previously only drawn on certain occasions, now it's drawn together with the sidebar.