Add error checking for thumbnail file migration

InvenTree/part/apps.py

@@ -30,6 +30,11 @@ class PartConfig(AppConfig):
                     
                     if not os.path.exists(loc):
                         print("InvenTree: Generating thumbnail for Part '{p}'".format(p=part.name))
-                        part.image.render_variations(replace=False)
+                        try:
+                            part.image.render_variations(replace=False)
+                        except FileNotFoundError:
+                            print("Image file missing")
+                            part.image = None
+                            part.save()
         except (OperationalError, ProgrammingError):
             print("Could not generate Part thumbnails")

InvenTree/part/migrations/0034_auto_20200404_1238.py

@@ -16,7 +16,14 @@ def create_thumbnails(apps, schema_editor):
         for part in Part.objects.all():
             # Render thumbnail for each existing Part 
             if part.image:
-                part.image.render_variations()
+                try:
+                    part.image.render_variations()
+                except FileNotFoundError:
+                    print("Missing image:", part.image())
+                    # The image is missing, so clear the field
+                    part.image = None
+                    part.save()
+                    
     except (OperationalError, ProgrammingError):
         # Migrations have not yet been applied - table does not exist
         print("Could not generate Part thumbnails")