Cygwin: is_console_app(): deal with the .bat/.cmd file extensions first

This function contains special handling of these file extensions,
treating them as console applications always, even if the first 1024
bytes do not contain a PE header with the console bits set.

However, Batch and Command files are never expected to have such a
header, therefore opening them and reading their first bytes is a waste
of time.

Let's honor the best practice to deal with easy conditions that allow
early returns first.

Fixes: bb42852 (Cygwin: pty: Implement new pseudo console suppot., 2020-08-19)
Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

winsup/cygwin/fhandler/termios.cc

@@ -704,6 +704,9 @@ fhandler_termios::fstat (struct stat *buf)
 static bool
 is_console_app (const WCHAR *filename)
 {
+  wchar_t *e = wcsrchr (filename, L'.');
+  if (e && (wcscasecmp (e, L".bat") == 0 || wcscasecmp (e, L".cmd") == 0))
+    return true;
   HANDLE h;
   h = CreateFileW (filename, GENERIC_READ, FILE_SHARE_READ,
 		   NULL, OPEN_EXISTING, 0, NULL);
@@ -720,9 +723,6 @@ is_console_app (const WCHAR *filename)
   IMAGE_NT_HEADERS32 *p = (IMAGE_NT_HEADERS32 *) memmem (buf, n, "PE\0\0", 4);
   if (p && (char *) &p->OptionalHeader.DllCharacteristics <= buf + n)
     return p->OptionalHeader.Subsystem == IMAGE_SUBSYSTEM_WINDOWS_CUI;
-  wchar_t *e = wcsrchr (filename, L'.');
-  if (e && (wcscasecmp (e, L".bat") == 0 || wcscasecmp (e, L".cmd") == 0))
-    return true;
   /* Return true for unknown to avoid standard handles from being unset.
      Setting-up standard handles for GUI apps is pointless, but not unsafe. */
   return true;