tal: make tal_len/tal_count(NULL) return 0.

Previously it crashed, but if you're always dealing with tal arrays,
this is painful.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/tal/tal.c

@@ -654,6 +654,9 @@ size_t tal_len(const tal_t *ptr)
 {
 	struct length *l;
 
+	if (!ptr)
+		return 0;
+
 	l = find_property(debug_tal(to_tal_hdr(ptr)), LENGTH);
 	if (!l)
 		return 0;

ccan/tal/tal.h

@@ -304,18 +304,18 @@ const char *tal_name(const tal_t *ptr);
 
 /**
  * tal_count - get the count of objects in a tal_arr.
- * @ptr: The tal allocated object array.
+ * @ptr: The tal allocated object array (or NULL)
  *
- * Returns 0 if @ptr has no length property, but be aware that that is
- * also a valid size!
+ * Returns 0 if @ptr has no length property or is NULL, but be aware
+ * that that is also a valid size!
  */
 #define tal_count(p) (tal_len(p) / sizeof(*p))
 
 /**
  * tal_len - get the count of bytes in a tal_arr.
- * @ptr: The tal allocated object array.
+ * @ptr: The tal allocated object array (or NULL)
  *
- * Returns 0 if @ptr has no length property, but be aware that that is
+ * Returns 0 if @ptr has no length property or NULL, but be aware that that is
  * also a valid size!
  */
 size_t tal_len(const tal_t *ptr);

ccan/tal/test/run-count.c

@@ -43,7 +43,11 @@ int main(void)
 
 	tal_set_backend(my_alloc, my_realloc, my_free, NULL);
 
-	plan_tests(19 * 3);
+	plan_tests(2 + 19 * 3);
+
+	p1 = NULL;
+	ok1(tal_len(p1) == 0);
+	ok1(tal_count(p1) == 0);
 
 	for (i = 0; i < 3; i++) {
 		move = i;

tools/depends.c

@@ -306,7 +306,7 @@ static char *get_one_ported(const void *ctx, const char *dir,
 	char **ported = get_one_prop(ctx, dir, "ported", get_info);
 
 	/* No news is good news. */
-	if (!ported || tal_count(ported) == 0)
+	if (tal_count(ported) == 0)
 		return NULL;
 
 	if (tal_count(ported) != 1)