qml: handle all possible QtMsgType in switch because of -Werror

Perhaps this illustrates why having -Werror is more of an annoyance
than whatever it was supposed to help:
https://codereview.qt-project.org/#change,65253

 cannot be merged
until the new enum value that it adds is handled _everywhere_ that
it can be.

Change-Id: I2bba730b471683487e38693c9ace2d09be4c874d
Reviewed-by: hjk <hjk121@nokiamail.com>