[assembler] Clippy: enable and fix must_use_candidate.

Author: youngman-g

assembler/src/asmlib/driver.rs

@@ -197,6 +197,7 @@ pub struct BinaryChunk {
 }
 
 impl BinaryChunk {
+    #[must_use]
     pub fn is_empty(&self) -> bool {
         self.words.is_empty()
     }

assembler/src/asmlib/lib.rs

@@ -1,5 +1,6 @@
 #![deny(unreachable_pub)]
 #![deny(unsafe_code)]
+#![warn(clippy::must_use_candidate)]
 
 mod ast;
 mod collections;

assembler/src/asmlib/readerleader.rs

@@ -180,6 +180,7 @@ fn test_bit_index() {
 /// 28, when the `☛☛PUNCH` directive includes a start address.  This
 /// may in fact be the case shown in the diagram on [page
 /// 6-23](https://archive.org/details/tx-2-users-handbook-nov-63/page/n175/mode/1up).
+#[must_use]
 pub fn reader_leader() -> Vec<Unsigned36Bit> {
     ([
         // These instructions are taken from the middle column of