Fix NPE when not recording data

Author: rhauch

build.properties

@@ -1,4 +1,4 @@
-strongback.version=1.2.0-Beta4
+strongback.version=1.2.0-Beta5
 #
 # The build will download a specific version of the WPILib given by the following URL
 # and install it into the 'libs/wpilib' folder. To use a different version of WPILib,

strongback/src/org/strongback/Strongback.java

@@ -717,9 +717,7 @@ public static void start() {
      * Same as {@link #start()}.
      *
      * @see #start()
-     * @deprecated
      */
-    @Deprecated
     public static void restart() {
         ENGINE.start();
     }
@@ -1368,7 +1366,7 @@ public synchronized boolean submit(Command command) {
         }
 
         public synchronized void flushRecorders() {
-            if (isRunning()) {
+            if (isRunning() && dataRecorderDriver != null) {
                 // Finally flush the data recorder ...
                 dataRecorderDriver.flush();
             }