Merge pull request #19762 from lukasalexanderweber:master

* Error Message for SURF if not implemented

In OpenCV 4.5.1 

import cv2 as cv
cv.xfeatures2d_SURF.create

will not create an AttributeError, even if the function is excluded (no nonfree option)

In Line 305 (now 306) however ´finder = FEATURES_FIND_CHOICES[args.features]()´ will raise an 

error: OpenCV(4.5.1) ..\opencv_contrib\modules\xfeatures2d\src\surf.cpp:1029: error: (-213:The function/feature is not implemented) This algorithm is patented and is excluded in this configuration; Set OPENCV_ENABLE_NONFREE CMake option and rebuild the library in function 'cv::xfeatures2d::SURF::create'

So we should check with cv.xfeatures2d_SURF.create() correctly if SURF is available

samples/python/stitching_detailed.py

@@ -29,8 +29,9 @@ BA_COST_CHOICES['no'] = cv.detail_NoBundleAdjuster
 
 FEATURES_FIND_CHOICES = OrderedDict()
 try:
+    cv.xfeatures2d_SURF.create() # check if the function can be called
     FEATURES_FIND_CHOICES['surf'] = cv.xfeatures2d_SURF.create
-except AttributeError:
+except (AttributeError, cv.error) as e:
     print("SURF not available")
 # if SURF not available, ORB is default
 FEATURES_FIND_CHOICES['orb'] = cv.ORB.create