Make sys_startgui() work again on Windows. Fixes #685.

7 jobs for startgui-windows-fix in 222 minutes and 54 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Test
passed debian_stretch_x86_64_deb #22244
debian stretch x86_64

00:35:06

passed osx_10.11_x86_64_dmg #22246
osx v10.11 dmg

00:20:49

passed osx_10.8_x86_64_dmg #22247
osx v10.8 dmg

00:19:02

canceled raspbian_stretch_armv7l_deb #22250
stretch arm raspbian

passed ubuntu_16.04_x86_64_deb #22245
ubuntu v16.04 x86_64

00:37:26

passed windows_i386_innosetup #22248
windows i386

01:50:30

failed raspbian_stretch_armv7l_deb #22249
raspbian arm stretch