Quick fix for Android-CI build.

Related to modernize-use-equals-default.

Source/Urho3D/Core/Variant.cpp

@@ -30,13 +30,13 @@
 namespace Urho3D
 {
 
-const Variant Variant::EMPTY;
-const PODVector<unsigned char> Variant::emptyBuffer;
-const ResourceRef Variant::emptyResourceRef;
-const ResourceRefList Variant::emptyResourceRefList;
+const Variant Variant::EMPTY { };
+const PODVector<unsigned char> Variant::emptyBuffer { };
+const ResourceRef Variant::emptyResourceRef { };
+const ResourceRefList Variant::emptyResourceRefList { };
 const VariantMap Variant::emptyVariantMap;
-const VariantVector Variant::emptyVariantVector;
-const StringVector Variant::emptyStringVector;
+const VariantVector Variant::emptyVariantVector { };
+const StringVector Variant::emptyStringVector { };
 
 static const char* typeNames[] =
 {

Source/Urho3D/Resource/JSONValue.cpp

@@ -53,7 +53,7 @@ static const char* numberTypeNames[] =
 };
 
 const JSONValue JSONValue::EMPTY;
-const JSONArray JSONValue::emptyArray;
+const JSONArray JSONValue::emptyArray { };
 const JSONObject JSONValue::emptyObject;
 
 JSONValue& JSONValue::operator =(bool rhs)