smurf: Fix compiler warning

In the default: case status is set bad but we still use the variables
later on without trapping for status. We initialise them here to prevent
the multiplication of uninitialised values. The alternative would be to
put status checking over more of the code.
smurf: New PWV conversion values

The conversion I have after cleaning the data using the rms are

9/21 to 1/18    pwv_befpre =  0.082403989+0.915565960*pwv_raw
1/19 to 2/28    pwv_before = 0.000062197+0.966982186*pwv_raw