AGS: Don't overflow when not scaling #340

Job	Run time
Xcode (macosx, -scheme ScummVM-macOS, --disable-nasm --enable-faad --enable-gif --enable-mikmod -...	33m 0s
Xcode (ios7, -scheme ScummVM-iOS CODE_SIGN_IDENTITY="" CODE_SIGNING_ALLOWED=NO, --use-xcframework...	38m 14s
Ubuntu (ubuntu-latest, sdl2-config, ccache g++, liba52-dev libcurl4-openssl-dev libfaad-dev libfl...	29m 57s
Ubuntu (ubuntu-20.04, sdl-config, ccache g++-4.8, g++-4.8 liba52-dev libcurl4-openssl-dev libfaad...	31m 15s
Windows (win32, x86-windows, x86, --enable-discord --enable-faad --enable-gif --enable-mikmod --e...	1h 2m 47s
Windows (x64, x64, x64-windows, --enable-discord --enable-faad --enable-gif --enable-mikmod --ena...	1h 5m 57s
Windows (arm64, arm64, arm64-windows, --enable-discord --enable-faad --enable-gif --enable-mikmod...	1h 20m 58s
	5h 42m 8s

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