[clang] Fix GCC -Wparentheses warning. NFC.
Without this gcc warned like:
clang/lib/Sema/SemaExprCXX.cpp:4656:74: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
4655 | From->isNullPointerConstant(Context,
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4656 | Expr::NPC_ValueDependentIsNull) &&
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
4657 | "Expr must be null pointer constant!");
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
