Merge pull request #19830 from alalek:issue_19368

modules/videoio/src/cap_dshow.cpp

@@ -2731,6 +2731,7 @@ int videoInput::start(int deviceID, videoDevice *VD){
     }
 
     VIDEOINFOHEADER *pVih =  reinterpret_cast<VIDEOINFOHEADER*>(VD->pAmMediaType->pbFormat);
+    CV_Assert(pVih);
     int currentWidth    =  HEADER(pVih)->biWidth;
     int currentHeight    =  HEADER(pVih)->biHeight;