DatabaseImagePersistenceStrategyTest: add code coverage for removeIfPossible() method.

No functional changes.

Author: php-coder

src/test/groovy/ru/mystamps/web/service/DatabaseImagePersistenceStrategyTest.groovy

@@ -166,4 +166,15 @@ class DatabaseImagePersistenceStrategyTest extends Specification {
 			result == expectedImageDto
 	}
 
+	//
+	// Tests for removeIfPossible()
+	//
+	
+	def 'removeIfPossible() should do nothing'() {
+		when:
+			strategy.removeIfPossible(null)
+		then:
+			noExceptionThrown()
+	}
+	
 }