reduce ssvWriter allocation in funcSort

mark             old ns/op     new ns/op     delta
BenchmarkFuncSort     1572          1413          -10.11%

benchmark             old allocs     new allocs     delta
BenchmarkFuncSort     8              7              -12.50%

benchmark             old bytes     new bytes     delta
benchmarkFuncSort     188           156           -17.02%

1 files changed, 7 insertions, 4 deletions

diff --git a/func.go b/func.go
index 550f67b..62e9af4 100644
--- a/func.go
+++ b/func.go
@@ -303,12 +303,15 @@ func (f *funcSort) Eval(w io.Writer, ev *Evaluator) {
 
 	// Remove duplicate words.
 	var prev string
-	sw := ssvWriter{w: w}
 	for _, tok := range toks {
-		if prev != tok {
-			sw.WriteString(tok)
-			prev = tok
+		if prev == tok {
+			continue
+		}
+		if prev != "" {
+			writeByte(w, ' ')
 		}
+		io.WriteString(w, tok)
+		prev = tok
 	}
 	addStats("funcbody", "sort", t)
 }