Answer
No. A civil case to declare the first marriage void is not a prejudicial question to a bigamy prosecution. Under Article 40 of the Family Code, a person must first obtain a judicial declaration of nullity of the first marriage before contracting a second one — he cannot decide for himself that the first marriage was void. So even if the first marriage is later declared void, the accused had already committed bigamy by remarrying without that prior judicial declaration.
The Supreme Court applied this in Marbella-Bobis v. Bobis (G.R. No. 138509) and Mercado v. Tan: a subsequent or pending nullity case does not suspend the bigamy case, because the crime of bigamy was already consummated when the second marriage was contracted without a prior judicial declaration that the first was void.