citra-qt: release all buttons when render window focus is lost

credit to @Hawkheart for the original idea

src/input_common/keyboard.cpp

@@ -53,6 +53,13 @@ public:
         }
     }
 
+    void ChangeAllKeyStatus(bool pressed) {
+        std::lock_guard<std::mutex> guard(mutex);
+        for (const KeyButtonPair& pair : list) {
+            pair.key_button->status.store(pressed);
+        }
+    }
+
 private:
     std::mutex mutex;
     std::list<KeyButtonPair> list;
@@ -79,4 +86,8 @@ void Keyboard::ReleaseKey(int key_code) {
     key_button_list->ChangeKeyStatus(key_code, false);
 }
 
+void Keyboard::ReleaseAllKeys() {
+    key_button_list->ChangeAllKeyStatus(false);
+}
+
 } // namespace InputCommon