Move Method shorty to managed heap

Change-Id: Iafd05502b498c823063d0603915a92db8c95f060
diff --git a/src/check_jni.cc b/src/check_jni.cc
index 0486284..38f47dc 100644
--- a/src/check_jni.cc
+++ b/src/check_jni.cc
@@ -446,7 +446,7 @@
   void checkSig(jmethodID mid, const char* expectedType, bool isStatic) {
     ScopedJniThreadState ts(mEnv);
     const Method* m = DecodeMethod(ts, mid);
-    if (*expectedType != m->GetShorty()[0]) {
+    if (*expectedType != m->GetShorty()->CharAt(0)) {
       LOG(ERROR) << "JNI ERROR: expected return type '" << *expectedType << "' calling " << PrettyMethod(m);
       JniAbort();
     } else if (isStatic && !m->IsStatic()) {