Update librustzcash dependency, address comments

depends/packages/librustzcash.mk

@@ -3,8 +3,8 @@ $(package)_version=0.1
 $(package)_download_path=https://github.com/zcash/$(package)/archive/
 $(package)_file_name=$(package)-$($(package)_git_commit).tar.gz
 $(package)_download_file=$($(package)_git_commit).tar.gz
-$(package)_sha256_hash=ed8de6f820f4441a80457a25db022168df09ca945302d27004975b0d71c32718
-$(package)_git_commit=0ef61e6d460e49e70202f8599bbdb2d39e41d061
+$(package)_sha256_hash=b96a0646d4c4856bc6171dc26cce10644a6129ac92b73a91f94246fb6b7f3516
+$(package)_git_commit=18f4945d942cc53e336c40bf13080934179a9047
 $(package)_dependencies=rust $(rust_crates)
 $(package)_patches=cargo.config
 

src/zcash/prf.cpp

@@ -13,7 +13,7 @@ std::array<unsigned char, 64> PRF_expand(const uint256& sk, unsigned char t)
     std::array<unsigned char, 64> res;   
     unsigned char blob[33];
 
-    memcpy(&blob[0], x.begin(), 32);
+    memcpy(&blob[0], sk.begin(), 32);
     blob[32] = t;
         
     crypto_generichash_blake2b_state state;
@@ -65,7 +65,7 @@ std::array<unsigned char, 11> default_diversifier(const uint256& sk)
         
         if (librustzcash_check_diversifier(res.data())) {
             break;
-        } else if (blob[33] > 255) {
+        } else if (blob[33] == 255) {
             throw std::runtime_error("librustzcash_check_diversifier did not return valid diversifier");
         }
         blob[33] += 1;