qmake SUBDIRS project incorrectly processes MAKEFILE specification

If a SUBDIRS project references the sub-project using the "<subproject>.file" specification, rather than the "<subproject>.subdir" specification, a "MAKEFILE" override in the sub-project's ".pro" file is not honoured correctly.

For example, if there is a SUBDIRS project, subdirs.pro, that uses:

SUBDIRS = subproject
subproject.file = subproject/subproject.pro

and a sub-project below it, subproject.pro, that specifies:

MAKEFILE=mysubproject.mak

then a "qmake -r subdirs.pro" causes "mysubproject.mak.mysubproject" to be generated, rather than "mysubproject.mak".

Example attached.