Auto merge of #17683 - birtles:tidy-list-length-check, r=emilio

Tidy up check for zero-length lists when interpolating

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Address feedback from https://github.com/servo/servo/pull/17613#discussion_r125775874

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- [ ] These changes fix #__ (github issue number if applicable).

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components/style/properties/helpers/animated_properties.mako.rs

@@ -826,7 +826,7 @@ macro_rules! repeated_vec_impl {
             fn add_weighted(&self, other: &Self, self_portion: f64, other_portion: f64)
                 -> Result<Self, ()> {
                 // If the length of either list is zero, the least common multiple is undefined.
-                if cmp::min(self.len(), other.len()) < 1 {
+                if self.is_empty() || other.is_empty() {
                     return Err(());
                 }
                 use num_integer::lcm;