[clang-tidy] Convert C casts to C++ ones

Found with google-readability-casting

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/wcstringutil.cpp

@@ -34,7 +34,7 @@ wcstring_range wcstring_tok(wcstring &str, const wcstring &needle, wcstring_rang
 }
 
 wcstring truncate(const wcstring &input, int max_len, ellipsis_type etype) {
-    if (input.size() <= (size_t)max_len) {
+    if (input.size() <= static_cast<size_t>(max_len)) {
         return input;
     }