[pkg/bytes] Fix "go test -race"

Go checks the pointers used, and it is required to follow the
rule #5 of "unsafe.Pointer" which requires to convert back
to "unsafe.Pointer" no later than in the same line where it was
converted to uintptr.

Signed-off-by: Dmitrii Okunev <xaionaro@meta.com>

Author: xaionaro

pkg/bytes/is_zero_filled_amd64.go

@@ -15,21 +15,33 @@ import (
 // IsZeroFilled returns true if b consists of zeros only.
 func IsZeroFilled(b []byte) bool {
 	hdr := (*reflect.SliceHeader)((unsafe.Pointer)(&b))
-	data := hdr.Data
+	data := unsafe.Pointer(hdr.Data)
 	length := hdr.Len
-	if data&0x07 != 0 {
+	if length == 0 {
+		return true
+	}
+
+	if uintptr(data)&0x07 != 0 {
 		// the data is not aligned, fallback to a simple way
 		return isZeroFilledSimple(b)
 	}
-	dataEnd := hdr.Data + uintptr(length)
-	dataWordsEnd := dataEnd & ^uintptr(0x07)
-	for ; data < dataWordsEnd; data += 8 {
-		if *(*uint64)(unsafe.Pointer(data)) != 0 {
+
+	dataEnd := uintptr(data) + uintptr(length)
+	dataWordsEnd := uintptr(dataEnd) & ^uintptr(0x07)
+	// example:
+	//
+	//     012345678901234567
+	//     wwwwwwwwWWWWWWWWtt : w -- word 0; W -- word 1; t -- tail
+	//                     ^
+	//                     |
+	//                     +-- dataWordsEnd
+	for ; uintptr(data) < dataWordsEnd; data = unsafe.Pointer(uintptr(data) + 8) {
+		if *(*uint64)(data) != 0 {
 			return false
 		}
 	}
-	for ; data < dataEnd; data++ {
-		if *(*uint8)(unsafe.Pointer(data)) != 0 {
+	for ; uintptr(data) < dataEnd; data = unsafe.Pointer(uintptr(data) + 1) {
+		if *(*uint8)(data) != 0 {
 			return false
 		}
 	}