sw: add test that SwXTextCursor is disposed if header is deleted

This test failed for 2 reasons:
1) since somewhere between LO 5.0 and 5.1, the PaMCorrAbs sent a
   SwMsgPoolItem but SwUnoCursorPointer checked for a LegacyModifyHint
   (fixed in commit a029a479)
2) the SwXHeadFootText being registered at the header format prevented
   its deletion (fixed in preceding commit)

Change-Id: I1d36bc2b9ca222b1b68fda94ded65451a677214a

sw/qa/extras/uiwriter/uiwriter.cxx

@@ -143,6 +143,7 @@ public:
     void testBookmarkUndo();
     void testFdo85876();
     void testFdo87448();
+    void testTextCursorInvalidation();
     void testTdf68183();
     void testCp1000115();
     void testTdf63214();
@@ -269,6 +270,7 @@ public:
     CPPUNIT_TEST(testBookmarkUndo);
     CPPUNIT_TEST(testFdo85876);
     CPPUNIT_TEST(testFdo87448);
+    CPPUNIT_TEST(testTextCursorInvalidation);
     CPPUNIT_TEST(testTdf68183);
     CPPUNIT_TEST(testCp1000115);
     CPPUNIT_TEST(testTdf63214);
@@ -1261,6 +1263,26 @@ void SwUiWriterTest::testFdo87448()
     CPPUNIT_ASSERT_MESSAGE(aMsg.getStr(), abs(nFirstEnd - nSecondEnd) < 10);
 }
 
+void SwUiWriterTest::testTextCursorInvalidation()
+{
+    createDoc();
+    SwDoc* pDoc = createDoc();
+    SwWrtShell* pWrtShell = pDoc->GetDocShell()->GetWrtShell();
+    uno::Reference<beans::XPropertySet> xPageStyle(getStyles("PageStyles")->getByName("Standard"), uno::UNO_QUERY);
+    CPPUNIT_ASSERT(xPageStyle.is());
+    xPageStyle->setPropertyValue("HeaderIsOn", uno::makeAny(true));
+    uno::Reference<text::XText> xHeader(getProperty<uno::Reference<text::XText>>(xPageStyle, "HeaderText"));
+    CPPUNIT_ASSERT(xHeader.is());
+    // create cursor inside the header text
+    uno::Reference<text::XTextCursor> xCursor(xHeader->createTextCursor());
+    // can't go right in empty header
+    CPPUNIT_ASSERT(!xCursor->goRight(1, false));
+// this does not actually delete the header:    xPageStyle->setPropertyValue("HeaderIsOn", uno::makeAny(false));
+    pWrtShell->ChangeHeaderOrFooter("Default Style", true, false, false);
+    // must be disposed after deleting header
+    CPPUNIT_ASSERT_THROW(xCursor->goRight(1, false), uno::RuntimeException);
+}
+
 void SwUiWriterTest::testTdf68183()
 {
     // First disable RSID and check if indeed no such attribute is inserted.