fixes #22360; compare with the half of randMax (#22361)

* fixes #22360; compare with the half of randMax

* add a test

(cherry picked from commit f3a7622514)

lib/pure/random.nim

@@ -381,10 +381,7 @@ proc rand*[T: Ordinal](r: var Rand; t: typedesc[T]): T {.since: (1, 7, 1).} =
   when T is range or T is enum:
     result = rand(r, low(T)..high(T))
   elif T is bool:
-    whenJsNoBigInt64:
-      result = (r.next or 0) < 0
-    do:
-      result = cast[int64](r.next) < 0
+    result = r.next < randMax div 2
   else:
     whenJsNoBigInt64:
       result = cast[T](r.next shr (sizeof(uint)*8 - sizeof(T)*8))

tests/stdlib/trandom.nim

@@ -282,3 +282,21 @@ block: # bug #17898
       for j in 0..<numRepeat:
         discard rands[i].next
         doAssert rands[i] notin randSet
+
+block: # bug #22360
+  const size = 1000
+  var fc = 0
+  var tc = 0
+
+  for _ in 1..size:
+    let s = rand(bool)
+
+    if s:
+      inc tc
+    else:
+      inc fc
+
+  when defined(js):
+    doAssert (tc, fc) == (483, 517), $(tc, fc)
+  else:
+    doAssert (tc, fc) == (510, 490), $(tc, fc)