vcbuild explodes is Python is not installed

[seishun]

• Version: master
• Platform: Windows 7
• Subsystem: build

If Python is not installed on the system, vcbuild prints out the following and creates a "Windows can't open this file" dialog

ERROR: The system was unable to find the specified registry key or value.
ERROR: The system was unable to find the specified registry key or value.
Cannot determine current version of Node.js

cc @refack

[addaleax]

There was a similar issue at yesterday’s code & learn, giving trouble when only Python 3 is installed I think?

/cc @hxlnt (assuming you might want to be cc’ed on these kinds of issues?)