[librsvg/librsvg-2.50] Comment on the extra block in to_computed_values so it doesn't get removed by accident.

[Federico Mena Quintero <federico src gnome org>]

commit 3ce21aa4b8c0334d5d4e16058d1ed494c8ea9e57
Author: Federico Mena Quintero <federico mena gmail com>
Date:   Thu Feb 25 20:31:24 2021 +0000

    Comment on the extra block in to_computed_values
    so it doesn't get removed by accident.

 rsvg_internals/src/properties.rs | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/rsvg_internals/src/properties.rs b/rsvg_internals/src/properties.rs
index b6e9324b..741a23d9 100644
--- a/rsvg_internals/src/properties.rs
+++ b/rsvg_internals/src/properties.rs
@@ -547,6 +547,10 @@ impl SpecifiedValues {
     pub fn to_computed_values(&self, computed: &mut ComputedValues) {
         macro_rules! compute {
             ($name:ident, $field:ident) => {{
+                // This extra block --------^
+                // is so that prop_val will be dropped within the macro invocation;
+                // otherwise all the temporary values cause this function to use
+                // an unreasonably large amount of stack space.
                 let prop_val = self.get_property(PropertyId::$name);
                 if let ParsedProperty::$name(s) = prop_val {
                     computed.set_value(ComputedValue::$name(