ntdll: Initialize the Length field of PEB->LdrData.

dlls/ntdll/thread.c

@@ -225,6 +225,7 @@ HANDLE thread_init(void)
     params.CurrentDirectory.DosPath.Buffer = current_dir;
     params.CurrentDirectory.DosPath.MaximumLength = sizeof(current_dir);
     params.wShowWindow = 1; /* SW_SHOWNORMAL */
+    ldr.Length = sizeof(ldr);
     RtlInitializeBitMap( &tls_bitmap, peb->TlsBitmapBits, sizeof(peb->TlsBitmapBits) * 8 );
     RtlInitializeBitMap( &tls_expansion_bitmap, peb->TlsExpansionBitmapBits,
                          sizeof(peb->TlsExpansionBitmapBits) * 8 );