Added NV12 support to fluid backend

modules/gapi/include/opencv2/gapi/fluid/gfluidbuffer.hpp

@@ -53,6 +53,10 @@ public:
 
         inline const uint8_t* linePtr(int index) const
         {
+            // "out_of_window" check:
+            // user must not request the lines which are outside of specified kernel window
+            GAPI_DbgAssert(index >= -m_border_size
+                        && index <  -m_border_size + static_cast<int>(m_linePtrs.size()));
             return m_linePtrs[index + m_border_size];
         }
     };

modules/gapi/include/opencv2/gapi/fluid/gfluidkernel.hpp

@@ -49,7 +49,8 @@ public:
     enum class Kind
     {
         Filter,
-        Resize
+        Resize,
+        NV12toRGB
     };
 
     // This function is a generic "doWork" callback