Fixed checkstyle warning (VariableDeclarationUsageDistance)

Author: brevilo

src/main/java/io/github/brevilo/jolm/Session.java

@@ -156,7 +156,7 @@ public boolean matchesInboundSessionFrom(String theirIdentityKey, String oneTime
    */
   public Message encrypt(String plainText) throws OlmException {
     // determine message type
-    NativeSize messageType = OlmLibrary.olm_encrypt_message_type(instance);
+    final NativeSize messageType = OlmLibrary.olm_encrypt_message_type(instance);
 
     // get native plain text
     Memory plainTextBuffer = Utils.toNative(plainText);