Add invalid data case to tdbstore ram init

Author: amq

features/storage/kvstore/tdbstore/TDBStore.cpp

@@ -938,6 +938,11 @@ int TDBStore::build_ram_table()
     offset = _master_record_offset;
 
     while (offset < _free_space_offset) {
+        if (offset == next_offset) {
+            ret = MBED_ERROR_INVALID_DATA_DETECTED;
+            goto end;
+        }
+
         ret = read_record(_active_area, offset, _key_buf, 0, 0, actual_data_size, 0,
                           true, false, false, true, hash, flags, next_offset);