[dart:io][windows] Stdout.supportsAnsiEscapes is false when not connected to a terminal

runtime/bin/stdio_win.cc

Index: runtime/bin/stdio_win.cc
diff --git a/runtime/bin/stdio_win.cc b/runtime/bin/stdio_win.cc
index 40df3a707beb4370409dba5e6298a84a76f8b04f..7e7690247f41c2656dbba99123acbfd48b324c91 100644
--- a/runtime/bin/stdio_win.cc
+++ b/runtime/bin/stdio_win.cc
@@ -92,12 +92,12 @@ bool Stdin::AnsiSupported(bool* supported) {
   HANDLE h = GetStdHandle(STD_INPUT_HANDLE);
   if (h == INVALID_HANDLE_VALUE) {
     *supported = false;
-    return false;
+    return true;
   }
   DWORD mode;
   if (!GetConsoleMode(h, &mode)) {
     *supported = false;
-    return false;
+    return true;
   }
   *supported = (mode & ENABLE_VIRTUAL_TERMINAL_INPUT) != 0;
   return true;
@@ -131,12 +131,12 @@ bool Stdout::AnsiSupported(intptr_t fd, bool* supported) {
   }
   if (h == INVALID_HANDLE_VALUE) {
     *supported = false;
-    return false;
+    return true;
   }
   DWORD mode;
   if (!GetConsoleMode(h, &mode)) {
     *supported = false;
-    return false;
+    return true;
   }
   *supported = (mode & ENABLE_VIRTUAL_TERMINAL_PROCESSING) != 0;
   return true;