Reassert the add equation in UIContext.
Reassert the add equation in UIContext.

Otherwise it might use subtract or some other equation.

Fixes another case of hrydgard/ppsspp#6678.

hrydgard/native,hrydgard/native,hrydgard/native,unknownbrackets/native,libretro/ppsspp-native,zhykzhykzhyk/ppsspp-native,unknownbrackets/native,libretro/ppsspp-native,zhykzhykzhyk/ppsspp-native,hrydgard/native,libretro/ppsspp-native,zhykzhykzhyk/ppsspp-native,zhykzhykzhyk/ppsspp-native,unknownbrackets/native,libretro/ppsspp-native,unknownbrackets/native