shell_windows: Get pid as uint32 instead int

os.Getppid() return int value but syscall.ProcessEntry32 struct have
`ProcessID` as uint32 so we are doing the type conversion as part of
`os.Getppid()` instead later in stage. It will fix following golint
error.
```
pkg/os/shell/shell_windows.go:33:38: G115: integer overflow conversion int -> uint32 (gosec)
                    if processEntry.ProcessID == uint32(pid) {
```

pkg/os/shell/shell_windows.go

@@ -1,6 +1,8 @@
 package shell
 
 import (
+	"fmt"
+	"math"
 	"os"
 	"path/filepath"
 	"strings"
@@ -13,7 +15,7 @@ var (
 )
 
 // re-implementation of private function in https://github.com/golang/go/blob/master/src/syscall/syscall_windows.go
-func getProcessEntry(pid int) (pe *syscall.ProcessEntry32, err error) {
+func getProcessEntry(pid uint32) (pe *syscall.ProcessEntry32, err error) {
 	snapshot, err := syscall.CreateToolhelp32Snapshot(syscall.TH32CS_SNAPPROCESS, 0)
 	if err != nil {
 		return nil, err
@@ -30,7 +32,7 @@ func getProcessEntry(pid int) (pe *syscall.ProcessEntry32, err error) {
 	}
 
 	for {
-		if processEntry.ProcessID == uint32(pid) {
+		if processEntry.ProcessID == pid {
 			pe = &processEntry
 			return
 		}
@@ -43,21 +45,25 @@ func getProcessEntry(pid int) (pe *syscall.ProcessEntry32, err error) {
 }
 
 // getNameAndItsPpid returns the exe file name its parent process id.
-func getNameAndItsPpid(pid int) (exefile string, parentid int, err error) {
+func getNameAndItsPpid(pid uint32) (exefile string, parentid uint32, err error) {
 	pe, err := getProcessEntry(pid)
 	if err != nil {
 		return "", 0, err
 	}
 
 	name := syscall.UTF16ToString(pe.ExeFile[:])
-	return name, int(pe.ParentProcessID), nil
+	return name, pe.ParentProcessID, nil
 }
 
 func detect() (string, error) {
 	shell := os.Getenv("SHELL")
 
 	if shell == "" {
-		shell, shellppid, err := getNameAndItsPpid(os.Getppid())
+		pid := os.Getppid()
+		if pid < 0 || pid > math.MaxUint32 {
+			return "", fmt.Errorf("integer overflow for pid: %v", pid)
+		}
+		shell, shellppid, err := getNameAndItsPpid(uint32(pid))
 		if err != nil {
 			return "cmd", err // defaulting to cmd
 		}

pkg/os/shell/shell_windows_test.go

@@ -1,6 +1,7 @@
 package shell
 
 import (
+	"math"
 	"os"
 	"testing"
 
@@ -18,15 +19,26 @@ func TestDetect(t *testing.T) {
 }
 
 func TestGetNameAndItsPpidOfCurrent(t *testing.T) {
-	shell, shellppid, err := getNameAndItsPpid(os.Getpid())
-
+	pid := os.Getpid()
+	if pid < 0 || pid > math.MaxUint32 {
+		assert.Fail(t, "integer overflow detected")
+	}
+	shell, shellppid, err := getNameAndItsPpid(uint32(pid))
 	assert.Equal(t, "shell.test.exe", shell)
-	assert.Equal(t, os.Getppid(), shellppid)
+	ppid := os.Getppid()
+	if ppid < 0 || ppid > math.MaxUint32 {
+		assert.Fail(t, "integer overflow detected")
+	}
+	assert.Equal(t, uint32(ppid), shellppid)
 	assert.NoError(t, err)
 }
 
 func TestGetNameAndItsPpidOfParent(t *testing.T) {
-	shell, _, err := getNameAndItsPpid(os.Getppid())
+	pid := os.Getppid()
+	if pid < 0 || pid > math.MaxUint32 {
+		assert.Fail(t, "integer overflow detected")
+	}
+	shell, _, err := getNameAndItsPpid(uint32(pid))
 
 	assert.Equal(t, "go.exe", shell)
 	assert.NoError(t, err)