Fix IOOBE in Repository.resolveSimple()

IndexOutOfBoundException is thrown from Repository.resolveSimple() when
'-g' string is located less then 4 characters from the end of this
string.

Change-Id: I1128c2cdfec9db3023d4d0f1f40d863e84b75950
Signed-off-by: Dariusz Luksza <dariusz@luksza.org>

org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java

@@ -597,7 +597,7 @@ public abstract class Repository {
 			return resolveAbbreviation(revstr);
 
 		int dashg = revstr.indexOf("-g");
-		if (4 < revstr.length() && 0 <= dashg
+		if ((dashg + 4) < revstr.length() && 0 <= dashg
 				&& isHex(revstr.charAt(dashg + 2))
 				&& isHex(revstr.charAt(dashg + 3))
 				&& isAllHex(revstr, dashg + 4)) {