fixes a collect() bug reported on the forum (#15156) [backport:1.2]

(cherry picked from commit 64aec6eb85)

compiler/semstmts.nim

@@ -161,7 +161,7 @@ proc semIf(c: PContext, n: PNode; flags: TExprFlags): PNode =
     if it.len == 2:
       openScope(c)
       it[0] = forceBool(c, semExprWithType(c, it[0]))
-      it[1] = semExprBranch(c, it[1])
+      it[1] = semExprBranch(c, it[1], flags)
       typ = commonType(typ, it[1])
       closeScope(c)
     elif it.len == 1:

lib/pure/sugar.nim

@@ -369,3 +369,13 @@ when isMainModule:
         of "bird": "word"
         else: d
     assert z == @["word", "word"]
+
+
+    proc tforum =
+      let ans = collect(newSeq):
+        for y in 0..10:
+          if y mod 5 == 2:
+            for x in 0..y:
+              x
+
+    tforum()