kpropertiesdialog: don't trip over malformed Exec
when the user incorrectly put env vars into the Program field the resulting desktop file will be somewhat malformed and literally contain
Exec='FOO=1 Bar'
this then needs careful handling when parsing so we don't accidentally drain the execline list. when this scenario appears we'll need to assume the last item in the list is the program as we can't really tell if it is a program that looks like an env var or an env var without program
BUG: 465290 (cherry picked from commit 78d43646)