Merge pull request #15111 from RealOrangeOne:patch-1

* Remove unavoidable print of CV error

The return value covers whether the device exists.

This might be better hidden behind a debug flag, but I couldn't work out how to do that nicely.

* Use `CV_LOG_WARNING` macro to log rather than removing it entirely

modules/videoio/src/cap_v4l.cpp

@@ -792,11 +792,10 @@ bool CvCaptureCAM_V4L::open(int _index)
         name = cv::format("/dev/video%d", _index);
     }
 
-    /* Print the CameraNumber at the end of the string with a width of one character */
     bool res = open(name.c_str());
     if (!res)
     {
-        fprintf(stderr, "VIDEOIO ERROR: V4L: can't open camera by index %d\n", _index);
+        CV_LOG_WARNING(NULL, cv::format("VIDEOIO ERROR: V4L: can't open camera by index %d", _index));
     }
     return res;
 }