1 bug fix in kernels.py

[amna-ukaea]

1) in ParsedAux in kernels.py there are many lines in the format string += f'variable={self.variable.name}\n', but one is written wrongly
before:
string += f'{self.function.str()}'

now:
string += f'function={self.function.str()}'
added "function=" so "function" is written to the file.

Also the same string written to file needs to be on separate lines, but one new line was missing
added new line in kernels.py because a new line was supposed to be there but wasn't_

before:
string += f'function={self.function.str()}

now:
string += f'function={self.function.str()}\n

2. in mesh.py the variable mesh is defined within the if statements inside the add_mesh_object method, but if none of the conditions are met, the variable remains undefined. Therefore, when you try to assign mesh to self.mesh_objects[name], it raises an UnboundLocalError.

before:
self.mesh_objects[name] = mesh

now:
mesh = None
if mesh is not None:
self.mesh_objects[name] = mesh