fix keyboard action

packages/zefyr/lib/src/widgets/toolbar.dart

     switch (platform) {
       case TargetPlatform.iOS:
       case TargetPlatform.android:
-        widget = hasOverlay ? buildButton(context, ZefyrToolbarAction.showKeyboard) : buildButton(context, ZefyrToolbarAction.hideKeyboard);
+        if (keyboardHeight > 0) {
+          widget = hasOverlay ? buildButton(context, ZefyrToolbarAction.showKeyboard) : buildButton(context, ZefyrToolbarAction.hideKeyboard);
+        } else {
+          widget = buildButton(context, ZefyrToolbarAction.showKeyboard);
+        }
         break;
       default:
         break;