log: use pointer instead of iterator

src/util/log.cc

@@ -152,7 +152,7 @@ void log_buf::realloc_buffer_and_append(char c) noexcept {
     _alloc_failure = true;
     std::string_view msg = "(log buffer allocation failure)";
     auto can_copy = std::min(msg.size(), size_t(_current - _begin));
-    std::memcpy(_current - can_copy, msg.begin(), can_copy);
+    std::memcpy(_current - can_copy, msg.data(), can_copy);
   }
 }