[vm] Fix broken failure code in Dwarf::WriteLineNumberProgram.

TEST=riscv64 build combined with CL 279174

Bug: https://github.com/dart-lang/sdk/issues/51051
Change-Id: I016f3a67510ea2a1fa8067aa61fa485ecb5cf172
Cq-Include-Trybots: luci.dart.try:vm-precomp-ffi-qemu-linux-release-riscv64-try,vm-kernel-precomp-asan-linux-release-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/279177
Commit-Queue: Tess Strickland <sstrickl@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>
diff --git a/runtime/vm/dwarf.cc b/runtime/vm/dwarf.cc
index 337d7ba..c01a496 100644
--- a/runtime/vm/dwarf.cc
+++ b/runtime/vm/dwarf.cc
@@ -896,10 +896,11 @@
                   script.ToCString());
           }
           // resolved_url is never obfuscated, so just convert the prefix.
-          auto const converted_cstr = ConvertResolvedURI(uri.ToCString());
+          auto const orig_cstr = uri.ToCString();
+          auto const converted_cstr = ConvertResolvedURI(orig_cstr);
           // Strictly enforce this to catch inconvertible cases.
           if (converted_cstr == nullptr) {
-            FATAL("cannot convert resolved URI %s", uri_cstr);
+            FATAL("cannot convert resolved URI %s", orig_cstr);
           }
           uri_cstr = converted_cstr;
         } else {