Submitted by cryptphi, also found by 0x1f8b and defsec
Project.sol#L887
Project.sol#L108-L115
It is possible to pass Signature Validity check with an SignatureDecoder.recoverKey() returns 0 whenever the builder and /or contractor have an existing approved hash for a data.
With occurrence of above, any user can call changeOrder or setComplete functions successfully after  user approves data hashes.
There should be a require check for _recoveredSignature != 0 in checkSignatureValidity().
parv3213 (Rigor) confirmed
