Fix validation while Shifting Bed

[Ashesh3]

Fixes coronasafe/care_fe#3072

The validation logic while shifting beds was recently updated in #731 , which included a query to check if any ConsultationBed exist and fetch the latest one.

This change fixes the way the existence of the object is checked.

exists() is a method of a QuerySet and hence would raise an Exception when called on latest object itself fetched from the .latest() method.

Now, the existence is checked first then the latest object is fetched, if exists.

qs = ConsultationBed.objects.filter(consultation=consultation)
# Validations based of the latest entry
if qs.exists():
    latest_qs = qs.latest("id")

[codecov-commenter]

Codecov Report

Merging #921 (aa77f60) into master (65184e2) will decrease coverage by 1.39%.
The diff coverage is 10.00%.

@@            Coverage Diff             @@
##           master     #921      +/-   ##
==========================================
- Coverage   54.24%   52.85%   -1.40%     
==========================================
  Files         181      181              
  Lines        8810     8813       +3     
==========================================
- Hits         4779     4658     -121     
- Misses       4031     4155     +124     

Impacted Files	Coverage Δ
care/facility/api/serializers/bed.py	40.70% <10.00%> (-0.37%)	⬇️
...e/utils/serializer/phonenumber_ispossible_field.py	50.00% <0.00%> (-43.75%)	⬇️
config/serializers.py	36.84% <0.00%> (-31.58%)	⬇️
care/audit_log/middleware.py	47.36% <0.00%> (-22.81%)	⬇️
care/users/models.py	73.75% <0.00%> (-16.32%)	⬇️
care/facility/models/mixins/permissions/base.py	45.00% <0.00%> (-15.00%)	⬇️
care/users/api/viewsets/users.py	43.50% <0.00%> (-12.34%)	⬇️
care/facility/api/viewsets/facility.py	58.10% <0.00%> (-12.17%)	⬇️
care/users/api/serializers/user.py	56.77% <0.00%> (-9.33%)	⬇️
care/facility/models/patient.py	88.09% <0.00%> (-6.75%)	⬇️
... and 7 more

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