src,crypto: refactor `crypto_dh.cc`
src,crypto: remove uses of AllocatedBuffer from crypto_dh.cc
Refs: https://github.com/nodejs/node/pull/39941
src: remove unnecessary static qualifier in crypto_dh.cc
ZeroPadDiffieHellmanSecret() is in an anonymous namespace, so it has
static linkage already.
src,crypto: handle empty maybe correctly in crypto_dh.cc
Buffer::Length() dereferences the passed Local, so calling it when the
underlying pointer is a nullptr would lead to a crash. This fixes that
by returning early instead.
Signed-off-by: Darshan Sen raisinten@gmail.com