BUG: Fix PythonQt light wrapping so that header in subfolder can be wrapped.

If path of the form "foo/bar.h" were considered for wrapping, the
test "IF (TMP_FILEPATH)" was returning true whereas the filepath
wasn't absolute.

This commit simplify the code and also make the test more robust by using
"IS_ABSOLUTE".
Merge branch 'fix-pythonqt-wrapping-with-subfolder'

* fix-pythonqt-wrapping-with-subfolder:
  BUG: Fix PythonQt light wrapping so that header in subfolder can be wrapped.