Now checking for peak and background selection. User reported crashed…

… in program that occured because he asked for a background subtraction but provided the same peak and background region... so no background region was extracted and then calculated...crashing the program. Now the program is catching for this problem and even if the user wants a background selection but gives me the same peak and back. region, no back is calculated. This refs #4303.

Code/Mantid/Framework/PythonAPI/PythonAlgorithms/RefLReduction.py

@@ -290,6 +290,18 @@ def PyExec(self):
         dMD = dSD + dSM
 
         ws_data = '_' + ws_name + '_DataWks'
+
+        #Even if user select Background subtraction
+        #make sure there is a background selection (peak != back selection)        
+
+        _LfromPx = data_back[0]
+        _LtoPx = data_peak[0]
+        _RfromPx = data_peak[1]
+        _RtoPx = data_back[1]
+
+        if ((_LfromPx == _LtoPx) and (_RfromPx == _RtoPx)):
+            subtract_data_bck = False
+
         if (subtract_data_bck and (backSubMethod == 1)):
 
             print '-> substract background'
@@ -455,7 +467,7 @@ def PyExec(self):
             else:
                 if (bLeftBack):
                     _y_px_range = _Larray
-                else:
+                else: 
                     _y_px_range = _Rarray
 
             for i in _tof_range:
@@ -518,8 +530,8 @@ def PyExec(self):
             ConvertToMatrixWorkspace(InputWorkspace=ws_data,
                                      OutputWorkspace=ws_data)
 
-            ConvertToMatrixWorkspace(InputWorkspace=ws_data,
-                                     OutputWorkspace=ws_data)
+#            ConvertToMatrixWorkspace(InputWorkspace=ws_data,
+#                                     OutputWorkspace=ws_data)
 
             if mtd.workspaceExists(ws_histo_data):
                 mtd.deleteWorkspace(ws_histo_data)