Fix some of the bugs found by this check

Author: franzpoeschel

examples/7_extended_write_serial.cpp

@@ -83,8 +83,9 @@ int main()
                 {{io::UnitDimension::M, 1}});
             electrons["displacement"]["x"].setUnitSI(1e-6);
             electrons.erase("displacement");
-            electrons["weighting"][io::RecordComponent::SCALAR].makeConstant(
-                1.e-5);
+            electrons["weighting"][io::RecordComponent::SCALAR]
+                .resetDataset({io::Datatype::FLOAT, {1}})
+                .makeConstant(1.e-5);
         }
 
         io::Mesh mesh = cur_it.meshes["lowRez_2D_field"];

examples/7_extended_write_serial.py

@@ -90,7 +90,9 @@
     electrons["displacement"].unit_dimension = {Unit_Dimension.M: 1}
     electrons["displacement"]["x"].unit_SI = 1.e-6
     del electrons["displacement"]
-    electrons["weighting"][SCALAR].make_constant(1.e-5)
+    electrons["weighting"][SCALAR] \
+        .reset_dataset(Dataset(np.dtype("float32"), extent=[1])) \
+        .make_constant(1.e-5)
 
     mesh = cur_it.meshes["lowRez_2D_field"]
     mesh.axis_labels = ["x", "y"]

examples/9_particle_write_serial.py

@@ -44,7 +44,9 @@
     # don't like it anymore? remove it with:
     # del electrons["displacement"]
 
-    electrons["weighting"][SCALAR].make_constant(1.e-5)
+    electrons["weighting"][SCALAR] \
+        .reset_dataset(Dataset(np.dtype("float32"), extent=[1])) \
+        .make_constant(1.e-5)
 
     particlePos_x = np.random.rand(234).astype(np.float32)
     particlePos_y = np.random.rand(234).astype(np.float32)