libmicrohttpd: 0.9.58 -> 0.9.59

Semi-automatic update. These checks were performed:

- built on NixOS
- found 0.9.59 with grep in /nix/store/vrgb5pfvbcn7f3c6gn4smc5w0xjmb6ss-libmicrohttpd-0.9.59
- found 0.9.59 in filename of file in /nix/store/vrgb5pfvbcn7f3c6gn4smc5w0xjmb6ss-libmicrohttpd-0.9.59

cc "@eelco @vrthra @fpletz"