RE 7210_MantidEV exception without peaks workspace

If the peaks workspace named on the MantidEV Find Peaks
tab does not exist, an error message will now be shown
AND the specified Q-vector will be displayed in the
table.  If the peaks workspace does exist, the
PointInfo() method the the workspace will be used, as
before.

refs #7210
Merge remote-tracking branch 'origin/bugfix/7210_MantidEV_exception_without_peaks_workspace'