Correct exception when rsa key not provided

[ehsannarmani]

When i provided rsa key is a empty string or something invalid thing, the purchase process is keep going until user payment, and after that purchaseFailed callback is calling with:
com.android.org.conscrypt.OpenSSLX509CertificateFactory$ParsingException: Error parsing public key

I suggest to check that rsa key before start purchase proccess and give a correct exception.

[hamid97m]

Thank you for your suggestion; we will fix this issue in the next version