dbghelp: Use debugstr_a() to trace a string that can be NULL.

dlls/dbghelp/dwarf.c

@@ -1920,7 +1920,7 @@ static struct symt* dwarf2_parse_subprogram(dwarf2_parse_context_t* ctx,
         inline_flags.u.uvalue != DW_INL_not_inlined)
     {
         TRACE("Function %s declared as inlined (%ld)... skipping\n",
-              name.u.string ? name.u.string : "(null)", inline_flags.u.uvalue);
+              debugstr_a(name.u.string), inline_flags.u.uvalue);
         return NULL;
     }