CapacityProjectSpreadsheet: set a 6 month due date only if date is due date is not set

If due date has an incorrect format it is better to fail than to hide
the error and produce wrong results.

dream/plugins/CapacityProjectSpreadsheet.py

@@ -25,11 +25,11 @@ class CapacityProjectSpreadsheet(plugin.InputPreparationPlugin):
                     projectId=projectData[row][0]
                     orderDate=strptime(projectData[row][1], '%Y/%m/%d')
                     orderDate=(orderDate-now).days 
-                    try:
+                    if projectData[row][2]:
                         dueDate=strptime(projectData[row][2], '%Y/%m/%d')
                         dueDate=(dueDate-now).days 
                     # if no due date is given set it to 180 (about 6 months)
-                    except ValueError:
+                    else:
                         dueDate=180
                     assemblySpaceRequirement=float(projectData[row][3])
                     capacityRequirementDict={}