[mythtv] Qt 3.0.5 and QVariant::isNull ()

[Bruce Markey]

The Qt 3.0.5 documentation doesn't have an isNull for
QVariant so compiles fail with 3.0.5 on:

tv_rec.cpp:969: no matching function for call to `QVariant::isNull ()'

I worked around this by changing

          if (query.value(0).isNull())
to:
          if (query.value(0) == "")

but is this a vaild subsitiution? It looks like it's going
to check for an int later and 0 would be a valid value.

--  bjm