fix: return correct error in find exec function and stat always

exec.go

@@ -172,7 +172,7 @@ func lookpath(file string) error { // custom lookpath function so we know if a c
 		if err == errNotExec {
 			return err
 		} else if err == nil {
-			return execName, nil
+			return nil
 		}
 	}
 

execfile_windows.go

@@ -3,14 +3,12 @@
 package main
 
 import (
-	"fmt"
 	"path/filepath"
 	"os"
 )
 
 func findExecutable(path string) error {
 	nameExt := filepath.Ext(path)
-
 	if nameExt == "" {
 		for _, ext := range filepath.SplitList(os.Getenv("PATHEXT")) {
 			_, err := os.Stat(path + ext)
@@ -18,10 +16,12 @@ func findExecutable(path string) error {
 				return nil
 			}
 		}
-	} else {
-		_, err := os.Stat(path)
-		return err
 	}
 
-	return errNotExec
+	_, err := os.Stat(path)
+	if err == nil {
+		return errNotExec
+	}
+
+	return os.ErrNotExist
 }