message: Don't query length() if we can use empty().
diff: @@ -179,10 +179,10 @@ std::string JoinPath(absl::string_view base, absl::string_view name) {
  // Make sure that we don't concatenation multiple superfluous separators.
  // Note, since we're using string_view, the substr() operations are cheap.
  - while (base.length() && base[base.length() - 1] == kFileSeparator[0]) {
  + while (!base.empty() && base[base.length() - 1] == kFileSeparator[0]) {
  base = base.substr(0, base.length() - 1);
  }
  - while (name.length() && name[0] == kFileSeparator[0]) {
  + while (!name.empty() && name[0] == kFileSeparator[0]) {
  name = name.substr(1);
  }
  return absl::StrCat(base, kFileSeparator, name);
  