AbstractUIDetails: fix potential comparison NPE

Theoretically, no object should have a null title. But just in case,
let's use the null-friendly MiscUtils.compare method for titles, too.

Author: ctrueden

src/main/java/org/scijava/AbstractUIDetails.java

@@ -235,7 +235,7 @@ public int compareTo(final Prioritized that) {
 		// compare titles
 		final String thisTitle = getTitle();
 		final String thatTitle = uiDetails.getTitle();
-		return thisTitle.compareTo(thatTitle);
+		return MiscUtils.compare(thisTitle, thatTitle);
 	}
 
 }