termstatus: Fix canUpdateStatus detection for redirected output

The canUpdateStatus check was simplified in #2608, but it accidentally flipped
the condition. The correct check is as follows: If the output is a pipe then
restic probably runs in mintty/cygwin. In that case it's possible to
update the output status. In all other cases it isn't.

This commit inverts to condition again to offer the previous and correct
behavior.

changelog/unreleased/issue-3111

@@ -0,0 +1,9 @@
+Bugfix: Correctly detect output redirection for `backup` command on Windows
+
+On Windows, since restic 0.10.0 the `backup` command did not properly detect
+when the output was redirected to a file. This caused restic to output
+terminal control characters. This has been fixed by correcting the terminal
+detection.
+
+https://github.com/restic/restic/issues/3111
+https://github.com/restic/restic/pull/3150

internal/ui/termstatus/terminal_windows.go

@@ -88,8 +88,8 @@ func canUpdateStatus(fd uintptr) bool {
 		return true
 	}
 
-	// check if the output file type is a pipe (0x0003)
-	if isPipe(fd) {
+	// check that the output file type is a pipe (0x0003)
+	if !isPipe(fd) {
 		return false
 	}