Fix Tree deserialization using JSON (#85)

* Closes #84

src/tree.rs

@@ -39,12 +39,28 @@ pub struct Tree<Pane> {
     pub tiles: Tiles<Pane>,
 
     /// When finite, this values contains the exact height of this tree
+    #[cfg_attr(
+        feature = "serde",
+        serde(deserialize_with = "deserialize_f32_null_as_infinity")
+    )]
     height: f32,
 
     /// When finite, this values contains the exact width of this tree
+    #[cfg_attr(
+        feature = "serde",
+        serde(deserialize_with = "deserialize_f32_null_as_infinity")
+    )]
     width: f32,
 }
 
+#[cfg(feature = "serde")]
+fn deserialize_f32_null_as_infinity<'de, D: serde::Deserializer<'de>>(
+    des: D,
+) -> Result<f32, D::Error> {
+    use serde::Deserialize;
+    Ok(Option::<f32>::deserialize(des)?.unwrap_or(f32::INFINITY))
+}
+
 impl<Pane: std::fmt::Debug> std::fmt::Debug for Tree<Pane> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         // Print a hierarchical view of the tree: