Use only a single instance for NLS translation bundles

As findbugs pointed out, there was a small risk for creating multiple instances of
translation bundles. If that happens, drop the second instance.

Change-Id: I3aacda86251d511f6bbc2ed7481d561449ce3b6c
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>

org.eclipse.jgit/src/org/eclipse/jgit/nls/NLS.java

@@ -125,11 +125,16 @@ public class NLS {
 		this.locale = locale;
 	}
 
+	@SuppressWarnings("unchecked")
 	private <T extends TranslationBundle> T get(Class<T> type) {
 		TranslationBundle bundle = map.get(type);
 		if (bundle == null) {
 			bundle = GlobalBundleCache.lookupBundle(locale, type);
-			map.putIfAbsent(type, bundle);
+			// There is a small opportunity for a race, which we may
+			// lose. Accept defeat and return the winner's instance.
+			TranslationBundle old = map.putIfAbsent(type, bundle);
+			if (old != null)
+				bundle = old;
 		}
 		return (T) bundle;
 	}