add testcase for #14227 (#15794)

tests/macros/t14227.nim

@@ -0,0 +1,23 @@
+discard """
+  action: "compile"
+"""
+import sugar
+
+
+block:
+  let y = @[@[1, 2], @[2, 4, 6]]
+  let x = collect(newSeq):
+    for i in y:
+      if i.len > 2:
+        for j in i:
+          j
+  echo(x)
+
+block:
+  let y = @[@[1, 2], @[2, 4, 6]]
+  let x = collect(newSeq):
+    for i in y:
+      for j in i:
+        if i.len > 2:
+          j
+  echo(x)