Importing invalid filetypes now gives proper error messages

CURA-2883

plugins/CuraProfileReader/CuraProfileReader.py

@@ -99,4 +99,6 @@ class CuraProfileReader(ProfileReader):
             return []
 
         filenames, outputs = profile_convert_funcs[0](serialized, profile_id)
+        if filenames is None and outputs is None:
+            return []
         return list(zip(outputs, filenames))

plugins/VersionUpgrade/VersionUpgrade21to22/Profile.py

@@ -5,6 +5,7 @@ import configparser #To read config files.
 import io #To write config files to strings as if they were files.
 
 import UM.VersionUpgrade
+from UM.Logger import Logger
 
 ##  Creates a new profile instance by parsing a serialised profile in version 1
 #   of the file format.
@@ -80,6 +81,7 @@ class Profile:
         import VersionUpgrade21to22 # Import here to prevent circular dependencies.
 
         if self._name == "Current settings":
+            Logger.log("w", "Unable to upgrade this profile. Skipping it.")
             return None, None #Can't upgrade these, because the new current profile needs to specify the definition ID and the old file only had the machine instance, not the definition.
 
         config = configparser.ConfigParser(interpolation = None)