Cryptomatte: Fix error loading incomplete metadata.

When rendering with cycles at some point the manifest is trimmed. This
leads to incomplete/corrupted metadata. This patch will make sure that
the manifest parser doesn't crash.

This solved the issue when the manifest is trimmed at the start of a
hash. Eg '"Name":"'.

source/blender/blenkernel/intern/cryptomatte.cc

@@ -425,6 +425,9 @@ static bool from_manifest(CryptomatteLayer &layer, blender::StringRefNull manife
       }
 
       const int quoted_hash_len = quoted_string_len_(ref);
+      if (quoted_hash_len < 2) {
+        return false;
+      }
       const int hash_len = quoted_hash_len - 2;
       CryptomatteHash hash = CryptomatteHash::from_hex_encoded(ref.substr(1, hash_len));
       ref = ref.drop_prefix(quoted_hash_len);