Potential issues from Coverity Static Analysis scan

[yashbhutwala]

I recently got a chance to run the bitcoin source code through Synopsys's static analysis tool, Coverity. I thought it'd be good to report some of the potential issues detected upstream. I am not a C++ expert, nor do I have the depth of the source-code here, so some of these may-be non-issues. Regardless, I'm reporting some of the "high" severity issues marked through the tool. Hoping someone with a deeper understanding of the code-base can better assess them and patch as necessary :)

https://github.com/bitcoin/bitcoin/blob/master/src/crypto/hmac_sha256.cpp#L14
and
https://github.com/bitcoin/bitcoin/blob/master/src/crypto/hmac_sha512.cpp#L14

https://github.com/bitcoin/bitcoin/blob/master/src/leveldb/table/table_builder.cc#L56

https://github.com/bitcoin/bitcoin/blob/master/src/leveldb/db/c.cc#L160

https://github.com/bitcoin/bitcoin/blob/master/src/key_io.cpp#L166 and https://github.com/bitcoin/bitcoin/blob/master/src/key_io.cpp#L189

There is also other "medium" and "low" severity issues that may or may not be patch worthy. If someone is interested, please email me or ping me on this issue.