Fix crash if a Context is stopped immediately after creation

src/main/java/com/team766/framework/Context.java

@@ -335,10 +335,10 @@ private void transferControl(final ControlOwner thisOwner, final ControlOwner de
      * This is the entry point for this Context's worker thread.
      */
     private void threadFunction() {
-        // OS threads run independently of one another, so we need to wait until
-        // the baton is passed to us before we can start running the user's code
-        waitForControl(ControlOwner.SUBROUTINE);
         try {
+            // OS threads run independently of one another, so we need to wait until
+            // the baton is passed to us before we can start running the user's code
+            waitForControl(ControlOwner.SUBROUTINE);
             // Call into the user's code.
             m_func.run(this);
             Logger.get(Category.FRAMEWORK)

src/test/java/com/team766/framework/ContextTest.java

@@ -0,0 +1,18 @@
+package com.team766.framework;
+
+import com.team766.TestCase;
+import org.junit.jupiter.api.Test;
+
+public class ContextTest extends TestCase {
+    /// Regression test: calling stop() on a Context before it is allowed to
+    /// run the first time should not crash the program.
+    @Test
+    public void testStopOnFirstTick() {
+        var lc = Scheduler.getInstance().startAsync(Procedure.NO_OP);
+        lc.stop();
+
+        step();
+
+        assertTrue(lc.isDone());
+    }
+}