reduce binary size of levenshtein

This removes the special handling for an empty first string,
which leads to an extra memory allocation in this case.
However this reduces the binary size noticeably:

opt-level=3:
961B strsim strsim::levenshtein
1.1KiB strsim strsim::levenshtein

opt-level=3
888B strsim strsim::levenshtein
949B strsim strsim::levenshtein

CHANGELOG.md

@@ -10,6 +10,8 @@ This project attempts to adhere to [Semantic Versioning](http://semver.org).
   - reduce runtime
   - reduce binary size by more than `25%`
 
+- reduce binary size of Levenshtein distance
+
 ### Fixed
 
 - Fix transposition counting in Jaro and Jaro-Winkler.

src/lib.rs

@@ -225,20 +225,16 @@ where
 {
     let b_len = b.into_iter().count();
 
-    if a.into_iter().next().is_none() {
-        return b_len;
-    }
-
     let mut cache: Vec<usize> = (1..b_len + 1).collect();
 
-    let mut result = 0;
+    let mut result = b_len;
 
     for (i, a_elem) in a.into_iter().enumerate() {
         result = i + 1;
         let mut distance_b = i;
 
         for (j, b_elem) in b.into_iter().enumerate() {
-            let cost = if a_elem == b_elem { 0usize } else { 1usize };
+            let cost = usize::from(a_elem != b_elem);
             let distance_a = distance_b + cost;
             distance_b = cache[j];
             result = min(result + 1, min(distance_a, distance_b + 1));