G-API: Recent inclusion has broken STANDALONE build

This MR fixes this.

modules/gapi/src/api/gbackend.cpp

@@ -94,8 +94,12 @@ void bindInArg(Mag& mag, const RcDesc &rc, const GRunArg &arg, bool is_umat)
         case GRunArg::index_of<cv::gapi::own::Mat>() :
             if (is_umat)
             {
+#if !defined(GAPI_STANDALONE)
                 auto& mag_umat = mag.template slot<cv::UMat>()[rc.id];
                 mag_umat = to_ocv(util::get<cv::gapi::own::Mat>(arg)).getUMat(ACCESS_READ);
+#else
+                util::throw_error(std::logic_error("UMat is not supported in stadnalone build"));
+#endif // !defined(GAPI_STANDALONE)
             }
             else
             {
@@ -157,8 +161,12 @@ void bindOutArg(Mag& mag, const RcDesc &rc, const GRunArgP &arg, bool is_umat)
         case GRunArgP::index_of<cv::gapi::own::Mat*>() :
             if (is_umat)
             {
+#if !defined(GAPI_STANDALONE)
                 auto& mag_umat = mag.template slot<cv::UMat>()[rc.id];
                 mag_umat = to_ocv(*(util::get<cv::gapi::own::Mat*>(arg))).getUMat(ACCESS_RW);
+#else
+                util::throw_error(std::logic_error("UMat is not supported in standalone build"));
+#endif // !defined(GAPI_STANDALONE)
             }
             else
             {
@@ -256,7 +264,13 @@ cv::GRunArgP getObjPtr(Mag& mag, const RcDesc &rc, bool is_umat)
     {
     case GShape::GMAT:
         if (is_umat)
+        {
+#if !defined(GAPI_STANDALONE)
             return GRunArgP(&mag.template slot<cv::UMat>()[rc.id]);
+#else
+            util::throw_error(std::logic_error("UMat is not supported in standalone build"));
+#endif //  !defined(GAPI_STANDALONE)
+        }
         else
             return GRunArgP(&mag.template slot<cv::gapi::own::Mat>()[rc.id]);
     case GShape::GSCALAR: return GRunArgP(&mag.template slot<cv::gapi::own::Scalar>()[rc.id]);
@@ -300,8 +314,12 @@ void writeBack(const Mag& mag, const RcDesc &rc, GRunArgP &g_arg, bool is_umat)
         }
         if (is_umat)
         {
+#if !defined(GAPI_STANDALONE)
             auto& in_mag = mag.template slot<cv::UMat>().at(rc.id);
             GAPI_Assert((out_arg_data == (in_mag.getMat(ACCESS_RW).data)) && " data for output parameters was reallocated ?");
+#else
+            util::throw_error(std::logic_error("UMat is not supported in standalone build"));
+#endif // !defined(GAPI_STANDALONE)
         }
         else
         {