Fix possible fiber task starvation issue that can occur (at least) af…

…ter an instrumented call site is invoked in 'finally' block (by @pron)

quasar-core/src/main/java/co/paralleluniverse/fibers/Fiber.java

@@ -786,6 +786,7 @@ boolean exec() {
                 }
             } finally {
                 state = State.TERMINATED;
+                task.setState(0);
                 monitorFiberTerminated(monitor);
                 setException(t);
             }