fix #135 : ensure || receives scalar logicals

A bug in `check_passed` was revealed while running
goodpractice tests with the experimental env variable
"_R_CHECK_LENGTH_1_LOGIC2_" = TRUE in R 3.6 (or during
devtools::check()).

The `chk` variable passed to `check_passed` can be of two
forms:

- a scalar (logical or NA); as returned in `chk_cyclocomp.R`;

- or a list(status = (logical or NA), positions = list(...))
  as returned in `chk_tnf.R`.

The scalar (first case) or the `status` entry indicates
whether the check passed

```
is.na(chk) || ("status" %in% names(chk) && is.na(chk[["status"]]))
```
caused the list-form of `chk` to throw the above error.

We now extract the `status` indicator from `chk` before
running the logical tests to see if the corresponding
checking function failed. This cleaned up the stream of
logical tests.

R/gp.R

@@ -62,13 +62,18 @@ gp <- function(path = ".", checks = all_checks(), extra_preps = NULL,
 }
 
 check_passed <- function(chk, na_as_passed = FALSE) {
-  if(na_as_passed){
-  isTRUE(chk) || ("status" %in% names(chk) && isTRUE(chk[["status"]])) || 
-    is.na(chk) || ("status" %in% names(chk) && is.na(chk[["status"]]))
+  status <- if ("status" %in% names(chk)) {
+    chk$status
   } else {
-    if (is.na(chk) || ("status" %in% names(chk) && is.na(chk[["status"]]))) 
-      return(NA)
-    isTRUE(chk) || ("status" %in% names(chk) && isTRUE(chk[["status"]]))
+    chk
+  }
+
+  if (na_as_passed) {
+    isTRUE(status) || is.na(status)
+  } else if (is.na(status)) {
+    NA
+  } else {
+    isTRUE(status)
   }
 }