"In a criminal trial, the defendant bears the burden of proving an affirmative defense. A court may determine whether an affirmative defense exists as a matter of law. We review a district court's conclusions of law for correctness. However, if there are conflicting facts regarding the availability of an affirmative defense in a criminal trial, the issue is properly submitted to a jury." State v. Leprowse, 2009 MT 387, ¶ 11, 353 Mont. 312, 221 P.3d 648 (internal citations omitted).