in fread integer64 argument is ignored if int64 type-bump occurs out-of-sample

[st-pasha]

dt0 = data.table(a=seq(10000), b="100")
dt0[111, b := "1000000000000"]
f = tempfile()
fwrite(dt0, f)

fread(f, integer64="numeric")
           a     b
       <int> <i64>
    1:     1   100
    2:     2   100
    3:     3   100
    4:     4   100
   ---            
 9996:  9996   100
 9997:  9997   100
 9998:  9998   100
 9999:  9999   100
10000: 10000   100

fread(f, integer64="character")
           a     b
       <int> <i64>
    1:     1   100
    2:     2   100
    3:     3   100
    4:     4   100
   ---            
 9996:  9996   100
 9997:  9997   100
 9998:  9998   100
 9999:  9999   100
10000: 10000   100