EachKey: do not allocate array if there is no need

parser.go

@@ -422,13 +422,15 @@ func EachKey(data []byte, cb func(int, []byte, ValueType, error), paths ...[]str
 				// for unescape: if there are no escape sequences, this is cheap; if there are, it is a
 				// bit more expensive, but causes no allocations unless len(key) > unescapeStackBufSize
 				var keyUnesc []byte
-				var stackbuf [unescapeStackBufSize]byte
 				if !keyEscaped {
 					keyUnesc = key
-				} else if ku, err := Unescape(key, stackbuf[:]); err != nil {
-					return -1
 				} else {
-					keyUnesc = ku
+					var stackbuf [unescapeStackBufSize]byte
+					if ku, err := Unescape(key, stackbuf[:]); err != nil {
+						return -1
+					} else {
+						keyUnesc = ku
+					}
 				}
 
 				if maxPath >= level {