`cord_internal`: fix a clang-tidy complaint about implicit bool conversions.

[`readability-implicit-bool-conversion`](https://clang.llvm.org/extra/clang-tidy/checks/readability/implicit-bool-conversion.html)
otherwise complains about this on upcoming commits.

PiperOrigin-RevId: 965931016
Change-Id: If5604471084217402b2bb4f64fd496d0749e802e

absl/strings/internal/cord_internal.h

diff --git a/absl/strings/internal/cord_internal.h b/absl/strings/internal/cord_internal.h
index 98dc4b5..5afb8cb 100644
--- a/absl/strings/internal/cord_internal.h
+++ b/absl/strings/internal/cord_internal.h
@@ -516,7 +516,7 @@
   // value. Creates an inlined SSO value if `rep` is null, otherwise
   // creates a tree instance value.
   constexpr InlineData(absl::string_view sv, CordRep* rep) noexcept
-      : rep_(rep ? Rep(rep) : Rep(sv)) {
+      : rep_(rep != nullptr ? Rep(rep) : Rep(sv)) {
     poison();
   }