fix FLUTTER_ANSI_TERMINAL check (#8544)

* fix FLUTTER_ANSI_TERMINAL check

should have been included in the previous PR :(

* review comments

bin/flutter.ps1

@@ -18,10 +18,11 @@ If (Test-Path Env:\FLUTTER_ANSI_TERMINAL) { Remove-Item Env:\FLUTTER_ANSI_TERMIN
 $stdout = [Win32.NativeMethods]::GetStdHandle(-11) # STD_OUTPUT_HANDLE
 If ($stdout -ne -1) {
     $mode = 0
-    $result = [Win32.NativeMethods]::GetConsoleMode($stdout, [ref]$mode)
-    If ($result) {
+    If ([Win32.NativeMethods]::GetConsoleMode($stdout, [ref]$mode)) {
         $mode = $mode -bor 4 # ENABLE_VIRTUAL_TERMINAL_PROCESSING
-        $env:FLUTTER_ANSI_TERMINAL = [Win32.NativeMethods]::SetConsoleMode($stdout, $mode)
+        If ([Win32.NativeMethods]::SetConsoleMode($stdout, $mode)) {
+            $env:FLUTTER_ANSI_TERMINAL = "true"
+        }
     }
 }
 

packages/flutter_tools/lib/src/base/logger.dart

@@ -245,8 +245,8 @@ class AnsiTerminal {
   AnsiTerminal() {
     String term = platform.environment['TERM'];
     // FLUTTER_ANSI_TERMINAL is a work-around for https://github.com/dart-lang/sdk/issues/28614
-    String flutterAnsiTerm =  platform.environment['FLUTTER_ANSI_TERMINAL'];
-    supportsColor = (term != null && term != 'dumb') || (flutterAnsiTerm != null);
+    bool flutterAnsiTerm = platform.environment.containsKey('FLUTTER_ANSI_TERMINAL');
+    supportsColor = (term != null && term != 'dumb') || flutterAnsiTerm;
   }
 
   static const String KEY_F1  = '\u001BOP';