@[] is a problem for --gc:destructors

Compile with `--gc:destructors`
```nim
import tables
var t = initTable[string, seq[ptr int]]()
discard t.hasKeyOrPut("f1", @[])
```
Lasted devel nim fails with error:
```
C:\Nim\x1.nim(3, 29) template/generic instantiation of `setLen` from here
C:\Nim\lib\core\seqs.nim(126, 11) Error: invalid type: 'empty' in this context: 'ptr NimSeqV2[empty]' for var
``