builtin random: Be less strict about arguments

This now allows:

- Same argument (`random 5 5`)
- Swapped ends (`random 10 2`)
- One possibility (`random 0 5 4`)

This makes it easier to use with numbers generated elsewhere instead
of hard-coded, so you don't need to check as much before running it.

Fixes #10879

src/builtins/random.rs

@@ -135,22 +135,14 @@ fn parse_ull(streams: &mut IoStreams, cmd: &wstr, num: &wstr) -> Result<u64, wut
         }
     }
 
-    if end <= start {
-        streams
-            .err
-            .append(wgettext_fmt!("%ls: END must be greater than START\n", cmd,));
-        return STATUS_INVALID_ARGS;
-    }
+    let (start, end) = if start <= end {
+        (start, end)
+    } else {
+        (end, start)
+    };
 
     // Using abs_diff() avoids an i64 overflow if start is i64::MIN and end is i64::MAX
     let possibilities = end.abs_diff(start) / step;
-    if possibilities == 0 {
-        streams.err.append(wgettext_fmt!(
-            "%ls: range contains only one possible value\n",
-            cmd,
-        ));
-        return STATUS_INVALID_ARGS;
-    }
 
     let rand = {
         let mut engine = RNG.lock().unwrap();