clang-tidy: Fix modernize-use-default-member-init in headers

See https://clang.llvm.org/extra/clang-tidy/checks/modernize/use-default-member-init.html

src/crypto/sha512.cpp

@@ -151,7 +151,7 @@ void Transform(uint64_t* s, const unsigned char* chunk)
 
 ////// SHA-512
 
-CSHA512::CSHA512() : bytes(0)
+CSHA512::CSHA512()
 {
     sha512::Initialize(s);
 }