File containing a single NA value is read as chr instead of logi

[st-pasha]

> str(fread("A\n\n"))
Classes ‘data.table’ and 'data.frame':	0 obs. of  1 variable:
 $ A: chr 
 - attr(*, ".internal.selfref")=<externalptr> 

Expected: a 1x1 data.table of logical type, instead getting a 0x1 data.table of character type.