AP_Logger: fix memory leak

libraries/AP_Logger/AP_Logger.cpp

@@ -1408,6 +1408,7 @@ void AP_Logger::log_file_content(const char *filename)
     const size_t len = strlen(filename)+1;
     char * tmp_filename = new char[len];
     if (tmp_filename == nullptr) {
+        delete file;
         return;
     }
     strncpy(tmp_filename, filename, len);