[REG: 4.1.0 -> 4.2.0]: Qt Creator crashes when opening a project file that contains reference to file that does not exist

Qt Creator crashes when loading a simple project file like:
SOURCES += "c:\file_that_does_not_exist.cpp"

The crash is not limited to SOURCES, also HEADERS and OTHER_FILES crash.

Qt Creator 4.1 did not crash in this situation. Also, if the backslash is replaced with forward slash, the crash does not occur. Crash does not happen at all if the file exists, even if backslash is used in the file path.

Steps to reproduce:

• Open the attached project file through Windows Explorer
• EXPECTED: Qt Creator parses the project and user can choose kits to continue
• ACTUAL: Qt Creator crashes while parsing the project file