Fix message systemd dropping final chunk unexpectedly

Signed-off-by: Lee Smet <lee.smet@hotmail.com>

mycelium/src/message.rs

@@ -440,7 +440,11 @@ where
                     return;
                 }
                 // Check max chunk idx.
-                let max_chunk_idx = message.len.div_ceil(MINIMUM_CHUNK_SIZE);
+                let max_chunk_idx = if message.len == 0 {
+                    0
+                } else {
+                    message.len.div_ceil(MINIMUM_CHUNK_SIZE) - 1
+                };
                 if mc.chunk_idx() > max_chunk_idx {
                     debug!("Dropping CHUNK because index is too high");
                     return;