pure_strcmp(): len(s2) can be > len(s1)

Reported by Antonio Morales from GitHub Security Labs, thanks!

src/utils.c

@@ -45,5 +45,11 @@ int pure_memcmp(const void * const b1_, const void * const b2_, size_t len)
 
 int pure_strcmp(const char * const s1, const char * const s2)
 {
-    return pure_memcmp(s1, s2, strlen(s1) + 1U);
+    const size_t s1_len = strlen(s1);
+    const size_t s2_len = strlen(s2);
+
+    if (s1_len != s2_len) {
+        return -1;
+    }
+    return pure_memcmp(s1, s2, s1_len);
 }