Fixed array offset in UtString.concat()

Author: dtim

utbot-framework/src/main/java/org/utbot/engine/overrides/strings/UtString.java

@@ -756,7 +756,7 @@ public String concat(String str) {
         }
         char[] newValue = new char[length + str.length()];
         UtArrayMock.arraycopy(value, 0, newValue, 0, length);
-        UtArrayMock.arraycopy(otherVal, 0, newValue, length + 1, str.length());
+        UtArrayMock.arraycopy(otherVal, 0, newValue, length, str.length());
         return new String(newValue);
     }