Merge pull request scratchfoundation#1305 from paulkaplan/fix-broadcast-wait

Fix tick yielding threads

Author: paulkaplan

src/engine/sequencer.js

@@ -221,6 +221,9 @@ class Sequencer {
                 // until the promise resolves. Promise resolution should reset
                 // thread.status to Thread.STATUS_RUNNING.
                 return;
+            } else if (thread.status === Thread.STATUS_YIELD_TICK) {
+                // stepThreads will reset the thread to Thread.STATUS_RUNNING
+                return;
             }
             // If no control flow has happened, switch to next block.
             if (thread.peekStack() === currentBlockId) {