read_log() seems broken when col_names specified but not col_types

[ilarischeinin]

read_log() works fine when no col_names argument is provided:

library(readr)
read_log(readr_example("example.log"))

Parsed with column specification:
cols(
  X1 = col_character(),
  X2 = col_character(),
  X3 = col_character(),
  X4 = col_character(),
  X5 = col_character(),
  X6 = col_integer(),
  X7 = col_integer()
)
# A tibble: 2 x 7
            X1    X2                 X3                         X4
         <chr> <chr>              <chr>                      <chr>
1 172.21.13.45  <NA> Microsoft\\JohnDoe 08/Apr/2001:17:39:04 -0800
2    127.0.0.1  <NA>              frank 10/Oct/2000:13:55:36 -0700
# ... with 3 more variables: X5 <chr>, X6 <int>, X7 <int>

But when col_names is provided, it fails:

read_log(readr_example("example.log"), col_names=c("ip", "identity", "user",
  "timestamp", "request", "status", "size"))

Error in .Call("readr_guess_types_", PACKAGE = "readr", sourceSpec, tokenizerSpec,  : 
  negative length vectors are not allowed

As the error comes when guessing column types, I tried to also provide col_types. This again works:

read_log(readr_example("example.log"), col_names=c("ip", "identity", "user",
  "timestamp", "request", "status", "size"), col_types=cols(ip=col_character(),
  identity=col_character(), user=col_character(), timestamp=col_character(),
  request=col_character(), status=col_integer(), size=col_integer()))

# A tibble: 2 x 7
            ip identity               user                  timestamp
         <chr>    <chr>              <chr>                      <chr>
1 172.21.13.45     <NA> Microsoft\\JohnDoe 08/Apr/2001:17:39:04 -0800
2    127.0.0.1     <NA>              frank 10/Oct/2000:13:55:36 -0700
# ... with 3 more variables: request <chr>, status <int>, size <int>

Searching the issues, I came across #331 and #403, which were fixed with #433. But with read_log(), this error still happens with version 1.0.0 from CRAN, or the current master branch (7dd808d). In this case it is also happens with a file with only two lines, whereas the other fix was for large files.