fix for test cases

lib/pure/collections/sequtils.nim

@@ -142,7 +142,7 @@ func concat*[T](seqs: varargs[seq[T]]): seq[T] =
       inc(i)
 
 func addUnique*[T](s: var seq[T], x: sink T) =
-  ## Adds `x` to the container `s` if it is not already present. 
+  ## Adds `x` to the container `s` if it is not already present.
   ## Uses `==` to check if the item is already present.
   runnableExamples:
     var a = @[1, 2, 3]
@@ -920,10 +920,11 @@ template foldl*(sequence, operation: untyped): untyped =
     assert concatenation == "nimiscool"
     assert foldl(procs, foo(a, b)) == "procIsAlsoFine"
 
-  assert sequence.len > 0, "Can't fold empty sequences"
+  let len = sequence.len
+  assert len > 0, "Can't fold empty sequences"
   var result: typeof(sequence[0])
   result = sequence[0]
-  for i in 1..<sequence.len:
+  for i in 1..<len:
     let
       a {.inject.} = result
       b {.inject.} = sequence[i]