Fix bug in runtime.memzero

Not the memory itself, but the byte after the memory was zeroed.

src/runtime/runtime.go

@@ -43,7 +43,7 @@ func memcpy(dst, src unsafe.Pointer, size uintptr) {
 // Set the given number of bytes to zero.
 func memzero(ptr unsafe.Pointer, size uintptr) {
 	for i := uintptr(0); i < size; i++ {
-		*(*byte)(unsafe.Pointer(uintptr(ptr) + size)) = 0
+		*(*byte)(unsafe.Pointer(uintptr(ptr) + i)) = 0
 	}
 }