python: also catch general c++ exceptions

they might be thrown from third-party code (notably Ogre in the ovis
module).
While Linux is kind enough to print them, they cause instant termination
on Windows.
Arguably, they do not origin from OpenCV itself, but still this helps
understanding what went wrong when calling an OpenCV function.

modules/python/src2/cv2.cpp

@@ -206,6 +206,11 @@ catch (const cv::Exception &e) \
 { \
     pyRaiseCVException(e); \
     return 0; \
+} \
+catch (const std::exception &e) \
+{ \
+    PyErr_SetString(opencv_error, e.what()); \
+    return 0; \
 }
 
 using namespace cv;