No warning if Info.xml not present
Using the 'nparts' option in FieldConvert it is possible to have a .fld file that may not contain a Info.xml file. Currently there is no check for this and so it causes a segment fault later in the code. We therefore need to check if the file exists and put in an Assert.
Possibly this is not an issue since in the case I was testing the info file was present but incorrect which is not something you can check for.