Make ASCII NUL imply Ctrl-Space instead of C-@

Seems mostly arbitrary.

termo.c

@@ -778,7 +778,15 @@ parse_multibyte (termo_t *tk, const unsigned char *bytes, size_t len,
 static void
 emit_codepoint (termo_t *tk, uint32_t codepoint, termo_key_t *key)
 {
-	if (codepoint < 0x20)
+	if (codepoint == 0)
+	{
+		// ASCII NUL = Ctrl-Space as well as Ctrl-@ but let's prefer
+		// the former to follow the behaviour of libtermkey
+		key->type = TERMO_TYPE_KEYSYM;
+		key->code.sym = TERMO_SYM_SPACE;
+		key->modifiers = TERMO_KEYMOD_CTRL;
+	}
+	else if (codepoint < 0x20)
 	{
 		// C0 range
 		key->code.codepoint = 0;

tests/02getkey.c

@@ -7,7 +7,7 @@ main (int argc, char *argv[])
 	termo_t *tk;
 	termo_key_t key;
 
-	plan_tests (38);
+	plan_tests (42);
 
 	tk = termo_new_abstract ("vt100", NULL, 0);
 
@@ -86,6 +86,15 @@ main (int argc, char *argv[])
 	is_int (key.modifiers, TERMO_KEYMOD_CTRL,
 		"key.modifiers after Ctrl-Escape");
 
+	termo_push_bytes (tk, "\0", 1);
+
+	is_int (termo_getkey (tk, &key), TERMO_RES_KEY,
+		"getkey yields RES_KEY after Ctrl-Space");
+
+	is_int (key.type, TERMO_TYPE_KEY, "key.type after Ctrl-Space");
+	is_int (key.code.codepoint, ' ', "key.code.codepoint after Ctrl-Space");
+	is_int (key.modifiers, TERMO_KEYMOD_CTRL, "key.modifiers after Ctrl-Space");
+
 	// Escape key in various amounts
 
 	termo_push_bytes (tk, "\x1b\x1b", 2);