tdf#92308: Dont crash on "File > Send > Email Document"

- crashed due to out-of-range index with empty vector
- kill pruposeless manual index fiddling for good
- add trivial test

Change-Id: Ic224c70f432d2b26718e05aa5a2742461cfb7bec
Reviewed-on: https://gerrit.libreoffice.org/16749Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>

sw/qa/core/uwriter.cxx

@@ -109,6 +109,7 @@ public:
     void testFormulas();
     void testIntrusiveRing();
     void testClientModify();
+    void testTdf92308();
 
     CPPUNIT_TEST_SUITE(SwDocTest);
 
@@ -141,6 +142,7 @@ public:
     CPPUNIT_TEST(testFormulas);
     CPPUNIT_TEST(testIntrusiveRing);
     CPPUNIT_TEST(testClientModify);
+    CPPUNIT_TEST(testTdf92308);
     CPPUNIT_TEST_SUITE_END();
 
 private:
@@ -1565,6 +1567,11 @@ void SwDocTest::testClientModify()
     CPPUNIT_ASSERT_EQUAL(aClient2.m_nNotifyCount,1);
 }
 
+void SwDocTest::testTdf92308()
+{
+    CPPUNIT_ASSERT_EQUAL(m_pDoc->HasInvisibleContent(), false);
+}
+
 void SwDocTest::setUp()
 {
     BootstrapFixture::setUp();

sw/source/core/doc/doc.cxx

@@ -1453,10 +1453,8 @@ bool SwDoc::HasInvisibleContent() const
         }
     }
 
-    const SwSectionFormats& rSectFormats = GetSections();
-    for( SwSectionFormats::size_type n = rSectFormats.size()-1; n; --n )
+    for(auto pSectFormat : GetSections())
     {
-        SwSectionFormat* pSectFormat = rSectFormats[ n ];
         // don't add sections in Undo/Redo
         if( !pSectFormat->IsInNodesArr())
             continue;