refactor: simplify encoded_varint64_len

This greatly cleans up the assembly as well, but this function is not
as likely to matter from a perf perspective.

protobuf/src/varint/encode.rs

@@ -59,12 +59,10 @@ pub(crate) fn encode_varint32(value: u32, buf: &mut [MaybeUninit<u8>]) -> usize
 /// Encoded size of u64 value.
 #[inline]
 pub(crate) fn encoded_varint64_len(value: u64) -> usize {
-    if value == 0 {
-        1
-    } else {
-        let significant_bits = 64 - value.leading_zeros();
-        (significant_bits + 6) as usize / 7
-    }
+    // Bitwise-or'ing by 1 allows the `value = zero` case to work without
+    // affecting other cases.
+    let significant_bits = 64 - (value | 1).leading_zeros();
+    (significant_bits + 6) as usize / 7
 }
 
 #[cfg(test)]