daemons: initialize libsodium at setup

According to the doc (https://download.libsodium.org/doc):
"sodium_init() initializes the library and should be called before
any other function provided by Sodium. [...]
the function ensures that the system's random number generator has
been properly seeded.".

common/daemon.c

@@ -11,6 +11,7 @@
 #include <common/utils.h>
 #include <common/version.h>
 #include <signal.h>
+#include <sodium.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/types.h>
@@ -146,6 +147,12 @@ void daemon_setup(const char *argv0,
 		memleak_init();
 #endif
 
+	/* We rely on libsodium for some of the crypto stuff, so we'd better
+	 * not start if it cannot do its job correctly. */
+	if (sodium_init() == -1)
+		errx(1, "Could not initialize libsodium. Maybe not enough entropy"
+		         " available ?");
+
 	/* We handle write returning errors! */
 	signal(SIGPIPE, SIG_IGN);
 	wally_init(0);