CommandModule: fix horrible bug in cancelation

If your Command implemented Cancelable, then calling cancel(...) from
within the command itself (e.g., from an initializer callback) did not
actually cancel anything, because the wrapping CommandModule instance
did not recognize the cancelation state of its wrapped Command.

Now, the CommandModule always leans on its wrapped Command for all
cancelation-related operations, unless the Command itself does not
implement Cancelable.

Noticed by Richard Domander. Thanks to Mark Hiner for help debugging.

Author: ctrueden

src/main/java/org/scijava/command/CommandModule.java

@@ -86,7 +86,11 @@ public class CommandModule extends AbstractModule implements Cancelable,
 	@Parameter
 	private Context context;
 
-	/** Reason for cancelation, or null if not canceled. */
+	/**
+	 * Reason for cancelation, or null if not canceled. Note that this field is
+	 * only relevant if the delegate {@link Command} is not itself
+	 * {@link Cancelable}.
+	 */
 	private String cancelReason;
 
 	/** Creates a command module for the given {@link PluginInfo}. */
@@ -205,20 +209,26 @@ public void run() {
 
 	@Override
 	public boolean isCanceled() {
+		if (command instanceof Cancelable) {
+			return ((Cancelable) command).isCanceled();
+		}
 		return cancelReason != null;
 	}
 
 	@Override
 	public void cancel(final String reason) {
-		cancelReason = reason == null ? "" : reason;
 		if (command instanceof Cancelable) {
-			// propagate cancelation to the command instance itself
 			((Cancelable) command).cancel(reason);
+			return;
 		}
+		cancelReason = reason == null ? "" : reason;
 	}
 
 	@Override
 	public String getCancelReason() {
+		if (command instanceof Cancelable) {
+			return ((Cancelable) command).getCancelReason();
+		}
 		return cancelReason;
 	}