encoding/base32: remove redundant conditional

Immediately following the conditional block removed here is a loop
which checks exactly what the conditional already checked, so the
entire conditional is redundant.

Change-Id: I892fd9f2364d87e2c1cacb0407531daec6643183
Reviewed-on: https://go-review.googlesource.com/114000Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/encoding/base32/base32.go

@@ -96,10 +96,6 @@ func (enc Encoding) WithPadding(padding rune) *Encoding {
 // so Encode is not appropriate for use on individual blocks
 // of a large data stream. Use NewEncoder() instead.
 func (enc *Encoding) Encode(dst, src []byte) {
-	if len(src) == 0 {
-		return
-	}
-
 	for len(src) > 0 {
 		var b [8]byte