Fix regression w/ templates defined in async proc

tests/async/ttemplateinasync.nim

@@ -0,0 +1,11 @@
+discard """
+  output: 42
+"""
+
+import asyncdispatch
+
+proc foo(): Future[int] {.async.} =
+  template ret() = return 42
+  ret()
+
+echo (waitFor foo())