Enrollment metrics - restructure queryset to avoid pylint failure

Author: johnbaldwin

figures/pipeline/enrollment_metrics.py

@@ -150,15 +150,18 @@ def collect_metrics_for_enrollment(course_enrollment, date_for=None, **_kwargs):
             course_enrollment.course_id))
 
     student_modules = student_modules_for_course_enrollment(ce=course_enrollment)
-
     if student_modules:
         most_recent_sm = student_modules.latest('modified')
     else:
         most_recent_sm = None
 
-    most_recent_lcgm = LearnerCourseGradeMetrics.objects.filter(
+    lcgm = LearnerCourseGradeMetrics.objects.filter(
         user=course_enrollment.user,
-        course_id=str(course_enrollment.course_id)).order_by('date_for').last()
+        course_id=str(course_enrollment.course_id))
+    if lcgm:
+        most_recent_lcgm = lcgm.latest('date_for')
+    else:
+        most_recent_lcgm = None
 
     if _enrollment_metrics_needs_update(most_recent_lcgm, most_recent_sm):
         progress_data = _collect_progress_data(most_recent_sm)