crypto: add null check to BIOPointer::New()

This function calls BIO_new() which mustn't receive a null pointer
argument. Yet it is able to handle null BIOs gracefully.
To solve this, add a null check.

Ref: nodejs/node#61788

Author: ndossche

src/ncrypto.cpp

@@ -1515,6 +1515,7 @@ BIOPointer BIOPointer::NewSecMem() {
 }
 
 BIOPointer BIOPointer::New(const BIO_METHOD* method) {
+  if (method == nullptr) return {};
   return BIOPointer(BIO_new(method));
 }