reflect: simplify array value comparable check

If array element is not interface, array or struct, we just need to
check whether the array element type is comparable.

Change-Id: I1ab94cfa17ae86feb6cd3fbdf878af5a776e7bec
Reviewed-on: https://go-review.googlesource.com/c/go/+/426194
Reviewed-by: Cherry Mui <[email protected]>
Run-TryBot: Cuong Manh Le <[email protected]>
Auto-Submit: Cuong Manh Le <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

src/reflect/value.go

@@ -3264,22 +3264,15 @@ func (v Value) Comparable() bool {
 		return true
 
 	case Array:
-		if v.Type().Len() == 0 {
-			return v.Type().Comparable()
-		}
-
 		switch v.Type().Elem().Kind() {
 		case Interface, Array, Struct:
 			for i := 0; i < v.Type().Len(); i++ {
 				if !v.Index(i).Comparable() {
 					return false
 				}
 			}
-		default:
-			return v.Index(0).Comparable()
 		}
-
-		return true
+		return v.Type().Comparable()
 
 	case Func:
 		return false