#39111: Product Collection - addMediaGalleryData calls getSize when the collection maybe or will be loaded (Can use count to avoid an extra DB query)

- Fixed call count instead of getSize if collection is loaded.

Author: Ihor Kh

app/code/Magento/Catalog/Test/Unit/Model/ResourceModel/Product/CollectionTest.php

@@ -311,7 +311,6 @@ public function testAddMediaGalleryData()
         $this->metadataPoolMock->expects($this->once())->method('getMetadata')->willReturn($metadataMock);
         $metadataMock->expects($this->once())->method('getLinkField')->willReturn($linkField);
 
-        $this->connectionMock->expects($this->once())->method('fetchOne')->with($selectMock)->willReturn(42);
         $this->connectionMock->expects($this->once())->method('fetchAll')->with($selectMock)->willReturn(
             [['row_id' => $rowId]]
         );