Fix coverity issues in the multi-dataset fit interface

[mantid-roman]

*** CID 1294007:  Uninitialized members  (UNINIT_CTOR)
/home/builder/jenkins-linode/workspace/coverity_build_and_submit/Code/Mantid/MantidQt/CustomInterfaces/src/MultiDatasetFit/MDFAddWorkspaceDialog.cpp: 37 in MantidQt::CustomInterfaces::MDF::AddWorkspaceDialog::AddWorkspaceDialog(QWidget *)()
31         }
32       }
33       connect(m_uiForm.cbWorkspaceName,SIGNAL(currentIndexChanged(const QString&)),this,SLOT(workspaceNameChanged(const QString&)));
34       m_uiForm.cbWorkspaceName->addItems( workspaceNames );
35     
36       connect(m_uiForm.cbAllSpectra,SIGNAL(stateChanged(int)),this,SLOT(selectAllSpectra(int)));
>>>     CID 1294007:  Uninitialized members  (UNINIT_CTOR)
>>>     Non-static class member "m_maxIndex" is not initialized in this constructor nor in any functions that it calls.
37     }
38     
39     /// Slot. Reacts on change of workspace name in the selection combo box.
40     /// @param wsName :: Name of newly selected workspace.
41     void AddWorkspaceDialog::workspaceNameChanged(const QString& wsName)
42     {

[mantid-roman]

This issue was originally trac ticket 11568