Merge pull request #11634 from vpisarev:empty_mat_with_types_2

fixes handling of empty matrices in some functions (#11634)

* a part of PR #11416 by Yuki Takehara

* moved the empty mat check in Mat::copyTo()

* fixed some test failures

modules/core/src/arithm.cpp

@@ -1233,6 +1233,12 @@ void cv::compare(InputArray _src1, InputArray _src2, OutputArray _dst, int op)
     CV_Assert( op == CMP_LT || op == CMP_LE || op == CMP_EQ ||
                op == CMP_NE || op == CMP_GE || op == CMP_GT );
 
+    if(_src1.empty() && _src2.empty())
+    {
+        _dst.release();
+        return;
+    }
+
     bool haveScalar = false;
 
     if ((_src1.isMatx() + _src2.isMatx()) == 1