Setting QtInstall to a path does not work

Steps to reproduce:

1. Create a new Qt GUI Application project
2. Open the project's properties, set "Qt Installation" to a path of a Qt installation

1. Try to compile the project

Compiling fails with

C:\Users\bkloster\AppData\Local\QtMsBuild\rcc\qtrcc.targets(109,5): error MSB3073: The command ""ERROR: Qt install dir not found\bin\rcc.exe" --list "QtGuiApplication3.qrc" > "Debug\rcc_list.txt" 2> nul" exited with code 123.

I believe the conditions for QtInstallDir in qt.props are incorrect. See the attached patch for a potential fix.