Make gitea work using cmd.exe again (#22073) (#22133)

Backport #22073

Gitea will attempt to lookup its location using LookPath however, this
fails on cmd.exe if gitea is in the current working directory.

exec.LookPath will return an exec.ErrDot error which we can test for and
then simply using filepath.Abs(os.Args[0]) to absolute gitea against the
current working directory.

Fix #22063

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/setting/setting.go

@@ -464,6 +464,13 @@ func getAppPath() (string, error) {
 		appPath, err = exec.LookPath(os.Args[0])
 	}
 
+	if err != nil {
+		// FIXME: Once we switch to go 1.19 use !errors.Is(err, exec.ErrDot)
+		if !strings.Contains(err.Error(), "cannot run executable found relative to current directory") {
+			return "", err
+		}
+		appPath, err = filepath.Abs(os.Args[0])
+	}
 	if err != nil {
 		return "", err
 	}