UIService: be careful setting status/progress

It is reasonable to want to reset only the status or progress of a UI
using a StatusEvent. However, the setting of both was being enforced by
the DefaultUIService's implementation.

Now, we check the received StatusEvent. The progress is only set if the
max is >= 0, and the message is only set if the string is not null.

Author: hinerm

src/main/java/org/scijava/ui/DefaultUIService.java

@@ -448,11 +448,16 @@ protected void onEvent(final StatusEvent event) {
 			final int val = event.getProgressValue();
 			final int max = event.getProgressMaximum();
 			final String message = getStatusMessage(event);
+			if (max < 0 && message == null) return;
 			for (UserInterface ui : getAvailableUIs()) {
 				final StatusBar statusBar = ui.getStatusBar();
 				if (statusBar != null) {
-					statusBar.setStatus(message);
-					statusBar.setProgress(val, max);
+					if (max >= 0) {
+						statusBar.setProgress(val, max);
+					}
+					if (message != null) {
+						statusBar.setStatus(message);
+					}
 				}
 			}
 		}