[ChangeLog][QtCore][QFileSelector] Removed the requirement for an unused
default base file in case you want to load only a variant.
When the base file (e.g. /image.jpg) was missing, no selectors were
considered and it was not possible to load variants of this file (e.g.
/+android/image.jpg, /+android/+tablet/image.jpg) without specifying the
directory as well.
As a work around, one previously had to place a default file in
the base location, which is undesirable in some cases because:
1. The extra file consumes unnecessary space.
2. It is impossible to encapsulate platform-specific implementation
details by hiding files in a subdirectory.
Task-number: QTBUG-51230
Change-Id: I4c7f9ec952bff6e5b7738d8cabe3c762c208a38e
Reviewed-by: Robin Burchell <robin.burchell@crimson.no>
da0241a2e7