Why was dharmendra not held guilty under hindu marriage act of 1955 section 17 and ipc section 494 for bigamy?

I do not want to get into other persons' affairs whether it is Dharmendra or anyone else. I shall state in general what happens. There are 2 types of offences under the law viz cognisable offences and non-cognisable offences. In the case of cognizable offences the State on its own should take cognisance of the offence and prosecute the offender. In the case of non-cognisable offences the State is not required to take up the case. The aggrieved party can file a criminal case if he or she feels aggrieved and proceed with the case. The question of a void marriage is relevant only when there are property interests

a hypothetical question, hence ignored.

are you aggrieved by this act of Dharmendra?, if yes then you can file criminal complaint 

This is not a hypothetical question. Dharmendra's instance is stated only as an example. If a person wants to know what is the position under law in such cases he can ask it here. There is no harm if this forum is used to gain knowledge.