fix: image placement when rotating (#493)

When rotating a partially shown image (i.e. image size * zoom >
window size) the image is panned to top or left (if `win->w` or
`win->h` is greatest, respectively). Seems to be due to
unsignedness of `win->[wh]`, when taking the difference between
them in `img_rotate` either `img->[xy]` ends up being close to
`UINT_MAX` and the image is panned to top or left edge.

Reviewed-on: https://codeberg.org/nsxiv/nsxiv/pulls/493
Reviewed-by: NRK <nrk@disroot.org>
Co-authored-by: e5150 <e5150@noreply.codeberg.org>
Co-committed-by: e5150 <e5150@noreply.codeberg.org>

image.c

@@ -676,8 +676,8 @@ void img_rotate(img_t *img, degree_t d)
 		ox = d == DEGREE_90  ? img->x : img->win->w - img->x - img->w * img->zoom;
 		oy = d == DEGREE_270 ? img->y : img->win->h - img->y - img->h * img->zoom;
 
-		img->x = oy + (img->win->w - img->win->h) / 2;
-		img->y = ox + (img->win->h - img->win->w) / 2;
+		img->x = oy + (int)(img->win->w - img->win->h) / 2;
+		img->y = ox + (int)(img->win->h - img->win->w) / 2;
 
 		tmp = img->w;
 		img->w = img->h;