Improve some asserts, minor fixes (theme, warnings) #10144

Job	Run time
build-windows (x64)	9m 5s
build-uwp	8m 21s
build-windows (ARM64)	9m 55s
build_test_headless_alpine	13m 38s
build (ubuntu-latest, test, clang, clang++, ./b.sh --headless --unittest, clang-normal)	5m 37s
build (ubuntu-latest, gcc, g++, ./b.sh --headless --unittest, gcc-normal)	5m 13s
build (ubuntu-latest, android, clang, clang++, cd android && ./ab.sh -j2 APP_ABI=arm64-v8a UNITTE...	10m 21s
build (ubuntu-latest, android, clang, clang++, cd android && ./ab.sh -j2 APP_ABI=armeabi-v7a UNIT...	8m 6s
build (ubuntu-latest, android, clang, clang++, cd android && ./ab.sh -j2 APP_ABI=x86_64 UNITTEST=...	9m 34s
build (ubuntu-latest, android, clang, clang++, cd android && ./ab.sh -j2 APP_ABI=arm64-v8a OPENXR...	9m 57s
build (ubuntu-latest, android, clang, clang++, ./b.sh --libretro_android ppsspp_libretro, android...	5m 51s
build (ubuntu-latest, qt, gcc, g++, ./b.sh --qt, qt)	5m 5s
build (ubuntu-latest, libretro, gcc, g++, make -C libretro -f Makefile -j2, gcc-libretro)	3m 32s
build (ubuntu-latest, libretro, clang, clang++, make -C libretro -f Makefile -j2, clang-libretro)	3m 58s
build (macos-latest, test, clang, clang++, ./b.sh --headless --unittest --fat --no-png --no-sdl2,...	8m 31s
build (macos-latest, ios, clang, clang++, ./b.sh --ios, ios)	5m 7s
test-windows	0s
test (ubuntu-latest)	50s
test (macos-latest)	32s
	2h 3m 13s

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