Move _STREAM_BOUNDARY before _STREAM_PART

The boundary delimiter (_STREAM_BOUNDARY) needs to be send before the
body part (_STREAM_PART) too follow RFC2046. This caused ffplay/ffmpeg
to fail to open the MJPEG stream.

Author: abergmann

README.md

@@ -212,6 +212,9 @@ esp_err_t jpg_stream_httpd_handler(httpd_req_t *req){
                 _jpg_buf = fb->buf;
             }
         }
+        if(res == ESP_OK){
+            res = httpd_resp_send_chunk(req, _STREAM_BOUNDARY, strlen(_STREAM_BOUNDARY));
+        }
         if(res == ESP_OK){
             size_t hlen = snprintf((char *)part_buf, 64, _STREAM_PART, _jpg_buf_len);
 
@@ -220,9 +223,6 @@ esp_err_t jpg_stream_httpd_handler(httpd_req_t *req){
         if(res == ESP_OK){
             res = httpd_resp_send_chunk(req, (const char *)_jpg_buf, _jpg_buf_len);
         }
-        if(res == ESP_OK){
-            res = httpd_resp_send_chunk(req, _STREAM_BOUNDARY, strlen(_STREAM_BOUNDARY));
-        }
         if(fb->format != PIXFORMAT_JPEG){
             free(_jpg_buf);
         }