Explicitly initialize OpenSSL with SSL proxy specs

Make sure we always initialize OpenSSL explicitly, even if there are no
certificates or keys loaded or generated.  Previously, OpenSSL would
only have been initialized if the configuration actually uses
certificates or keys, which is not always the case, e.g. with -t
pointing to an empty directory.

Issue:		#92
Reported by:	xelalexv

main.c

@@ -696,6 +696,11 @@ main(int argc, char *argv[])
 		spec->natsocket = nat_getsocketcb(spec->natengine);
 	}
 	if (opts_has_ssl_spec(opts)) {
+		if (ssl_init() == -1) {
+			fprintf(stderr, "%s: failed to initialize OpenSSL.\n",
+			                argv0);
+			exit(EXIT_FAILURE);
+		}
 		if ((opts->cacrt || !opts->tgcrtdir) && !opts->cakey) {
 			fprintf(stderr, "%s: no CA key specified (-k).\n",
 			                argv0);