Use 1. as initial mass matrix if grad is zero

Author: aseyboldt

src/adapt_strategy.rs

@@ -352,7 +352,8 @@ impl<F: CpuLogpFunc> AdaptStrategy for ExpWindowDiagAdapt<F> {
             state
                 .grad
                 .iter()
-                .map(|&grad| Some((grad).abs().recip().clamp(LOWER_LIMIT, UPPER_LIMIT))),
+                .map(|&grad| grad.abs().recip().clamp(LOWER_LIMIT, UPPER_LIMIT))
+                .map(|var| if var.is_finite() { Some(var) } else { Some(1.) })
         );
     }