build,win: fix python detection script

Handle spaces in the path to python.exe, in case it is installed
under some directory like "C:\Program Files".

PR-URL: https://github.com/nodejs/node/pull/14546
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

tools/msvs/find_python.cmd

@@ -41,7 +41,7 @@ EXIT /B 1
 :validate
 IF NOT EXIST "%p%python.exe" EXIT /B 1
 :: Check if %p% is python2
-%p%python.exe -V 2>&1 | findstr /R "^Python.2.*" > NUL
+"%p%python.exe" -V 2>&1 | findstr /R "^Python.2.*" > NUL
 IF ERRORLEVEL 1 EXIT /B %ERRORLEVEL%
 :: We can wrap it up
 ENDLOCAL & SET pt=%p%& SET need_path_ext=%need_path%