Remove warning about unused fields (#116)

more safety checks around malloc and removes unused variable

src/ChunkPrinter.cpp

@@ -34,7 +34,6 @@ size_t ChunkPrinter::write(uint8_t c)
 
 size_t ChunkPrinter::write(const uint8_t *buffer, size_t size)
 {
-  esp_err_t err;
   size_t written = 0;
 
   while (written < size)

src/PsychicFileResponse.cpp

@@ -104,9 +104,16 @@ esp_err_t PsychicFileResponse::send()
   if (size < FILE_CHUNK_SIZE)
   {
     uint8_t *buffer = (uint8_t *)malloc(size);
-    int readSize = _content.readBytes((char *)buffer, size);
+    if (buffer == NULL)
+    {
+      /* Respond with 500 Internal Server Error */
+      httpd_resp_send_err(this->_request->request(), HTTPD_500_INTERNAL_SERVER_ERROR, "Unable to allocate memory.");
+      return ESP_FAIL;
+    }
+
+    size_t readSize = _content.readBytes((char *)buffer, size);
 
-    this->setContent(buffer, size);
+    this->setContent(buffer, readSize);
     err = PsychicResponse::send();
 
     free(buffer);