MAGETWO-69107: [Backport] - [Magento Cloud] Switching stores not working properly - for 2.1

- Fix store switcher

Author: danielrenaud

app/code/Magento/Store/Model/Store.php

@@ -1160,18 +1160,29 @@ public function getCurrentUrl($fromStore = true)
         if (!$this->isUseStoreInUrl()) {
             $storeParsedQuery['___store'] = $this->getCode();
         }
+
         if ($fromStore !== false) {
             $storeParsedQuery['___from_store'] = $fromStore ===
                 true ? $this->_storeManager->getStore()->getCode() : $fromStore;
         }
 
+        $requestStringParts = explode('?', $requestString, 2);
+        $requestStringPath = $requestStringParts[0];
+        if (isset($requestStringParts[1])) {
+            parse_str($requestStringParts[1], $requestString);
+        } else {
+            $requestString = [];
+        }
+
+        $currentUrlQueryParams = array_merge($requestString, $storeParsedQuery);
+
         $currentUrl = $storeParsedUrl['scheme']
             . '://'
             . $storeParsedUrl['host']
             . (isset($storeParsedUrl['port']) ? ':' . $storeParsedUrl['port'] : '')
             . $storeParsedUrl['path']
-            . $requestString
-            . ($storeParsedQuery ? '?' . http_build_query($storeParsedQuery, '', '&') : '');
+            . $requestStringPath
+            . ($currentUrlQueryParams ? '?' . http_build_query($currentUrlQueryParams, '', '&') : '');
 
         return $currentUrl;
     }