Fix crash on no translation in entity_load producer

[OleksiiTsulun]

Fixes bug when entity_load data producer tries to get entity's translation without checking if translation exists.

[codecov]

Codecov Report

Merging #1016 into 8.x-4.x will decrease coverage by 0.31%.
The diff coverage is 75.00%.

@@              Coverage Diff              @@
##             8.x-4.x    #1016      +/-   ##
=============================================
- Coverage      54.74%   54.43%   -0.32%     
- Complexity       626      627       +1     
=============================================
  Files            113      113              
  Lines           1569     1580      +11     
=============================================
+ Hits             859      860       +1     
- Misses           710      720      +10     

Impacted Files	Coverage Δ	Complexity Δ
.../Plugin/GraphQL/DataProducer/Entity/EntityLoad.php	90.90% <75.00%> (-4.10%)	14.00 <0.00> (+1.00)	⬇️
src/Plugin/GraphQL/Schema/SdlSchemaPluginBase.php	41.50% <0.00%> (-4.33%)	19.00% <0.00%> (ø%)
...n/GraphQL/DataProducer/EntityDefinition/Fields.php	0.00% <0.00%> (ø)	12.00% <0.00%> (ø%)
...L/SchemaExtension/SdlSchemaExtensionPluginBase.php	0.00% <0.00%> (ø)	5.00% <0.00%> (ø%)

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[klausi]

Makes sense!

Can you add some test coverage? In EntityTest.php we already have a bit of coverage for languages.