add timespec_empty()

src/timespec.c

@@ -216,6 +216,14 @@ bool timespec_clear_spec(struct mgos_timespec *ts) {
   return true;
 }
 
+// Return true if the timespec is empty
+bool timespec_empty(struct mgos_timespec *ts) {
+  if (!ts) {
+    return true;
+  }
+  return SLIST_EMPTY(&ts->specs);
+}
+
 // Return a null terminated string in 'ret' of max retlen-1 which is a
 // comma separated set of timespec elements from the linked list.
 // Returns true on success, false otherwise.