Do not fail hard if preplots do not exist.

They might not have been done yet, and it will be obvious
to the user if they're not there.

bin/import_preplots.py

@@ -8,6 +8,7 @@ or modified preplots and (re-)import them into the database.
 """
 
 from glob import glob
+import sys
 import configuration
 import preplots
 from datastore import Datastore
@@ -28,7 +29,12 @@ if __name__ == '__main__':
 			print(f"Preplot: {file['path']}")
 			if not db.file_in_db(file["path"]):
 				print("Importing")
-				preplot = preplots.from_file(file)
+				try:
+					preplot = preplots.from_file(file)
+				except FileNotFoundError:
+					print(f"File does not exist: {file['path']}", file=sys.stderr)
+					continue
+
 				if type(preplot) is list:
 					print("Saving to DB")
 					db.save_preplots(preplot, file["path"], file["class"], survey["epsg"])