core: fix String::end() implementation

modules/core/include/opencv2/core/cvstd.hpp

@@ -748,7 +748,7 @@ const char* String::begin() const
 inline
 const char* String::end() const
 {
-    return len_ ? cstr_ + 1 : 0;
+    return len_ ? cstr_ + len_ : NULL;
 }
 
 inline

modules/core/test/test_misc.cpp

@@ -138,3 +138,10 @@ TEST(Core_String, find_last_of__with__empty_string)
     // npos is not exported: EXPECT_EQ(cv::String::npos, p);
     EXPECT_EQ(std::string::npos, p);
 }
+
+TEST(Core_String, end_method_regression)
+{
+    cv::String old_string = "012345";
+    cv::String new_string(old_string.begin(), old_string.end());
+    EXPECT_EQ(6u, new_string.size());
+}