largefiles: explicitly set the source and sink types to 'hg' for lfconvert

I stumbled into this prior to adding the type indicator on the source and sink,
but there's no reason to try to infer the types for this conversion.

hgext/largefiles/lfcommands.py

@@ -177,7 +177,7 b' def lfconvert(ui, src, dest, *pats, **op'
             convcmd.converter = converter
 
             try:
-                convcmd.convert(ui, src, dest)
+                convcmd.convert(ui, src, dest, source_type='hg', dest_type='hg')
             finally:
                 convcmd.converter = orig
         success = True