Valgrind: Return correct row count from ErrorListModel.

Inexplicably, the current implementation returns 1 if the error list is
empty, which results in a bogus entry in the view and is sure to confuse
people to the point that they might think the analyzer is not working at
all (I know I did).

Change-Id: I9f5999f859347993b012c408129f18260a8c2bea
Reviewed-by: hjk <hjk121@nokiamail.com>