fix(main_loop): Tell miner to continue in race-condition case

In the case where the miner sends main loop something that doesn't build
on tip (block proposal or new block), the miner waits for main loop to
tell it to continue, but prior to this commit, that message never came.

src/main_loop.rs

@@ -497,6 +497,7 @@ impl MainLoopHandler {
 
                 if !global_state_mut.incoming_block_is_more_canonical(&new_block) {
                     warn!("Got new block from miner task that was not child of tip. Discarding.");
+                    self.main_to_miner_tx.send(MainToMiner::Continue);
                     return Ok(());
                 } else {
                     info!(
@@ -547,6 +548,7 @@ impl MainLoopHandler {
                            slow to competitively compose blocks. Consider running the client only \
                            with the guesser flag set and not the compose flag."
                     );
+                    self.main_to_miner_tx.send(MainToMiner::Continue);
                     return Ok(());
                 }