Merge pull request #8288 from Jejos:bugfix_medianBlur_accessviolation

diff --combined modules/imgproc/src/smooth.cpp
index 8ee49fa,7efa56c..d9c88d6
--- 1/modules/imgproc/src/smooth.cpp
--- 2/modules/imgproc/src/smooth.cpp
+++ b/modules/imgproc/src/smooth.cpp
@@@ -1677,7 -1677,7 +1677,7 @@@ namespace c
  
          try
          {
 -            ivx::Context ctx = ivx::Context::create();
 +            ivx::Context ctx = ovx::getOpenVXContext();
              if ((vx_size)(ksize.width) > ctx.convolutionMaxDimension() || (vx_size)(ksize.height) > ctx.convolutionMaxDimension())
                  return false;
  
@@@ -2239,7 -2239,7 +2239,7 @@@ static bool openvx_gaussianBlur(InputAr
  
      try
      {
 -        ivx::Context ctx = ivx::Context::create();
 +        ivx::Context ctx = ovx::getOpenVXContext();
          if ((vx_size)(ksize.width) > ctx.convolutionMaxDimension() || (vx_size)(ksize.height) > ctx.convolutionMaxDimension())
              return false;
  
@@@ -3361,7 -3361,7 +3361,7 @@@ namespace c
  
          try
          {
 -            ivx::Context ctx = ivx::Context::create();
 +            ivx::Context ctx = ovx::getOpenVXContext();
  #ifdef VX_VERSION_1_1
              if ((vx_size)ksize > ctx.nonlinearMaxDimension())
                  return false;
@@@ -3494,7 -3494,7 +3494,7 @@@ void cv::medianBlur( InputArray _src0, 
  
      CV_Assert( (ksize % 2 == 1) && (_src0.dims() <= 2 ));
  
-     if( ksize <= 1 )
+     if( ksize <= 1 || _src0.empty() )
      {
          _src0.copyTo(_dst);
          return;