fdo76734-Text Box is not preserved for file created in MSWord 2007.

Issue:Only one AlternateContent is getting written in the RT file irrespective of
the number of TextBoxes in the original file which is causing the issue.
RootCause is found in DocxAttributeOutput::OutputFlyFrame_Impl where under case
sw::Frame::eTxtBox,m_aFramesOfParagraph.push_back(sw::Frame(rFrame)); is getting executed only once.
push_back should happen as many number of times as there are TextBoxes in the original file.

if(rFrame.GetFrmFmt().GetName() == m_aFramesOfParagraph[nIndex].GetFrmFmt().GetName())
	bDuplicate = true;

In the above check both the GetName() are returning values as empty which leads to
bDuplicate equals TRUE and hence push_back does not happen.
I have introduced one more check to handle this.

Also changes are made in for loop to make it more efficient.

Conflicts:
	sw/qa/extras/ooxmlexport/ooxmlexport.cxx
Reviewed on:
	https://gerrit.libreoffice.org/8782

Change-Id: I397aa3c4548cb57e8dacbf3fbf9ebaf87c0daa80