Initialize the obs_cinipos in case there is no background attribute in...

Initialize the obs_cinipos in case there is no background attribute in obsvect. With this version of the code, I could run the flexpart test using Espen data

pycif/plugins/obsoperators/fp/obsoper.py

@@ -286,7 +286,8 @@ def obsoper(self, inputs, mode,
 
                     obs_cinipos[obs_i] = np.dot(cini[:],
                                                 controlvect.x[npvar+ni*ncini:npvar+(ni+1)*ncini])
-
+            else:
+                obs_cinipos[:]=0
 
             if getattr(tracer, 'offsets', False):
                 # Optimize offsets