Generic forms: Don't raise, display exceptions

Update the generic single object create and edit views to display
critical exceptions instead of just raising them and stoping
execution. The should allow removing duplicated exception to message
code in subclasses of these views.

Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>

mayan/apps/common/generics.py

@@ -355,6 +355,9 @@ class SingleObjectCreateView(ObjectNameMixin, ViewPermissionCheckMixin, ExtraCon
                     'error': exception
                 }
             )
+            return super(
+                SingleObjectCreateView, self
+            ).form_invalid(form=form)
         else:
             context = self.get_context_data()
 
@@ -452,8 +455,9 @@ class SingleObjectEditView(ObjectNameMixin, ViewPermissionCheckMixin, ObjectPerm
                     'error': exception
                 }
             )
-
-            raise exception
+            return super(
+                SingleObjectEditView, self
+            ).form_invalid(form=form)
         else:
             messages.success(
                 self.request,