Initialize all variables

Set m_isFolder = false also in "close" method

Fixes: QTBUG-80468
Change-Id: I5449692d61d4d340e83bdca337b86e054e8bf561
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/plugins/platforms/android/qandroidassetsfileenginehandler.cpp

@@ -288,6 +288,7 @@ public:
             m_assetFile = 0;
             return true;
         }
+        m_isFolder = false;
         return false;
     }
 
@@ -397,9 +398,9 @@ public:
 
 private:
     AAsset *m_assetFile = nullptr;
-    AAssetManager *m_assetManager;
+    AAssetManager *m_assetManager = nullptr;
     QString m_fileName;
-    bool m_isFolder;
+    bool m_isFolder = false;
 };