Fix oddness check in MyersDiff for negative numbers

It's probably not possible that these numbers are negative in the
algorithm, but it's cleaner this way and gets rid of three more
FindBugs warnings.

Change-Id: Ifbce4e2c787fb9a7cd309c605e8d86211ef8a352

org.eclipse.jgit/src/org/eclipse/jgit/diff/MyersDiff.java

@@ -300,7 +300,7 @@ public class MyersDiff<S extends Sequence> {
 
 			final int getIndex(int d, int k) {
 // TODO: remove
-if (((d + k - middleK) % 2) == 1)
+if (((d + k - middleK) % 2) != 0)
 	throw new RuntimeException(MessageFormat.format(JGitText.get().unexpectedOddResult, d, k, middleK));
 				return (d + k - middleK) / 2;
 			}
@@ -472,7 +472,7 @@ if (k < beginK || k > endK)
 				if (k < backward.beginK || k > backward.endK)
 					return false;
 				// TODO: move out of loop
-				if (((d - 1 + k - backward.middleK) % 2) == 1)
+				if (((d - 1 + k - backward.middleK) % 2) != 0)
 					return false;
 				if (x < backward.getX(d - 1, k))
 					return false;
@@ -514,7 +514,7 @@ if (k < beginK || k > endK)
 				if (k < forward.beginK || k > forward.endK)
 					return false;
 				// TODO: move out of loop
-				if (((d + k - forward.middleK) % 2) == 1)
+				if (((d + k - forward.middleK) % 2) != 0)
 					return false;
 				if (x > forward.getX(d, k))
 					return false;