Cygwin: console: Fix segfault on shared_console_info access.

- Accessing shared_console_info before initialization causes access
  violation because it is a NULL pointer. The cause of the problem
  reported in https://cygwin.com/ml/cygwin/2020-02/msg00197.html is
  this NULL pointer access in request_xterm_mode_output() when it is
  called from close(). This patch makes sure that shared_console_info
  is not NULL before calling request_xterm_mode_output().

winsup/cygwin/fhandler_console.cc

@@ -1159,18 +1159,17 @@ fhandler_console::close ()
 
   acquire_output_mutex (INFINITE);
 
-  if (shared_console_info && myself->pid == con.owner &&
-      wincap.has_con_24bit_colors () && !con_is_legacy)
-    request_xterm_mode_output (false);
-
-  /* Restore console mode if this is the last closure. */
-  OBJECT_BASIC_INFORMATION obi;
-  NTSTATUS status;
-  status = NtQueryObject (get_handle (), ObjectBasicInformation,
-			  &obi, sizeof obi, NULL);
-  if (NT_SUCCESS (status) && obi.HandleCount == 1)
-    if (wincap.has_con_24bit_colors ())
-      request_xterm_mode_output (false);
+  if (shared_console_info && wincap.has_con_24bit_colors ())
+    {
+      /* Restore console mode if this is the last closure. */
+      OBJECT_BASIC_INFORMATION obi;
+      NTSTATUS status;
+      status = NtQueryObject (get_handle (), ObjectBasicInformation,
+			      &obi, sizeof obi, NULL);
+      if ((NT_SUCCESS (status) && obi.HandleCount == 1)
+	  || myself->pid == con.owner)
+	request_xterm_mode_output (false);
+    }
 
   release_output_mutex ();
 

winsup/cygwin/release/3.1.5

@@ -5,3 +5,7 @@ Bug Fixes:
   Don't move cursor to the right in case of a NUL character in the console
   output stream, this is not backed by terminfo.
   Addresses: https://cygwin.com/ml/cygwin/2020-02/msg00162.html
+
+- Fix a segfault when starting, e.g., mintty from a bash in a console
+  running xterm emulation.
+  Addresses: https://cygwin.com/ml/cygwin/2020-02/msg00197.html