ACP2E-1958: avoid reloading configs for each requested key; added unit tests

Author: alzota

lib/internal/Magento/Framework/App/DeploymentConfig.php

@@ -185,7 +185,7 @@ private function getEnvOverride() : array
      */
     private function reloadInitialData(): void
     {
-        if (empty($this->readerLoad)) {
+        if (empty($this->readerLoad) || empty($this->data) || empty($this->flatData)) {
             $this->readerLoad = $this->reader->load();
         }
         $this->data = array_replace(

lib/internal/Magento/Framework/App/Test/Unit/DeploymentConfigTest.php

@@ -228,7 +228,7 @@ public function keyCollisionDataProvider(): array
      */
     public function testResetData(): void
     {
-        $this->readerMock->expects($this->exactly(1))->method('load')->willReturn(self::$fixture);
+        $this->readerMock->expects($this->exactly(2))->method('load')->willReturn(self::$fixture);
         $this->assertSame(self::$flattenedFixture, $this->deploymentConfig->get());
         $this->deploymentConfig->resetData();
         // second time to ensure loader will be invoked only once after reset