Fix empty authentication info check

[lucamrgs]

Authentication information is an optional property. Currently, no authentication information corresponds to an empty authentication information struct passed to the capability.Execute() function, so it is always passed as either a populated or empty authentication information struct.

Http.utils addAuthTo function checks if authentication information is passed, by checking if it has nil value, or not. If it has nil value, then no auth headers are added, and no further auth info checks are performed.

The bug is in the fact that authentication information will never be "nil", but either a completely empty struct, or a non-completely empty struct. Hence it is always != "nil", and subsequent checks fail.

In this MR, the check is changed to compare the authentication information (passed to Execute for http and OpenC2 capabilities) to an empty struct, instead of to nil value.