Make fn WeightedTreeIndex::try_sample public

rand_distr/src/weighted_tree.rs

@@ -247,7 +247,7 @@ impl<W: Clone + PartialEq + PartialOrd + SampleUniform + SubAssign<W> + Weight>
     ///
     /// Returns an error if there are no elements or all weights are zero. This
     /// is unlike [`Distribution::sample`], which panics in those cases.
-    fn try_sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Result<usize, WeightError> {
+    pub fn try_sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Result<usize, WeightError> {
         let total_weight = self.subtotals.first().cloned().unwrap_or(W::ZERO);
         if total_weight == W::ZERO {
             return Err(WeightError::InsufficientNonZero);