fix(logging): Corrected FPS calculation

Previously, last_frame was only updated once at the beginning of stream_handler,
leading to incorrect FPS and avg_frame_time computation.

This commit ensures last_frame is updated on each iteration after last FPS computation,
resulting in accurate FPS logging.

Fixes espressif#10920

Author: TNeutron

libraries/ESP32/examples/Camera/CameraWebServer/app_httpd.cpp

@@ -216,12 +216,8 @@ static esp_err_t stream_handler(httpd_req_t *req) {
   size_t _jpg_buf_len = 0;
   uint8_t *_jpg_buf = NULL;
   char *part_buf[128];
-
   static int64_t last_frame = 0;
-  if (!last_frame) {
-    last_frame = esp_timer_get_time();
-  }
-
+  
   res = httpd_resp_set_type(req, _STREAM_CONTENT_TYPE);
   if (res != ESP_OK) {
     return res;
@@ -236,6 +232,11 @@ static esp_err_t stream_handler(httpd_req_t *req) {
 #endif
 
   while (true) {
+    
+    if (!last_frame) {
+    last_frame = esp_timer_get_time();
+    }
+
     fb = esp_camera_fb_get();
     if (!fb) {
       log_e("Camera capture failed");