Fixes a nimsuggest crash when using chronos

The following would crash nimsuggest on init:
```
import chronos
type
  HistoryQuery = object
    start: int
    limit: int

  HistoryResult = object
    messages: string

type HistoryQueryHandler* = proc(req: HistoryQuery): Future[HistoryResult] {.async, gcsafe.}
```

compiler/semtypes.nim

@@ -2180,6 +2180,10 @@ proc semTypeNode(c: PContext, n: PNode, prev: PType): PType =
     else:
       let symKind = if n.kind == nkIteratorTy: skIterator else: skProc
       result = semProcTypeWithScope(c, n, prev, symKind)
+      if result == nil:
+        localError(c.config, n.info, "type expected, but got: " & renderTree(n))
+        result = newOrPrevType(tyError, prev, c)
+
       if n.kind == nkIteratorTy and result.kind == tyProc:
         result.flags.incl(tfIterator)
       if result.callConv == ccClosure and c.config.selectedGC in {gcArc, gcOrc, gcAtomicArc}: