Restore producing thumbnails while loading legacy reports #586

Job	Run time
build-macos-no-brew (clang-9)	16m 5s
build-macos-no-brew (clang-9)	16m 5s
build-macos-brew (clang-9)	5m 57s
build-macos-brew (clang-9)	5m 57s
build-linux (gcc-9)	13m 37s
build-linux (gcc-9)	13m 37s
build-macos-brew-Qt6 (clang-9)	8m 29s
build-macos-brew-Qt6 (clang-9)	8m 29s
build-linux-Qt6 (gcc-9)	15m 4s
build-linux-Qt6 (gcc-9)	15m 4s
build-macos-no-brew-Qt6 (clang-9)	22m 36s
build-macos-no-brew-Qt6 (clang-9)	22m 36s
build-windows-mingw (5.15.2)	3m 33s
build-windows-mingw (5.15.2)	14m 27s
build-windows-vs (5.15.2)	14m 32s
build-windows-vs (5.15.2)	14m 32s
build-windows-mingw-Qt6 (6.3.0, qtmultimedia qt5compat)	12m 13s
build-windows-mingw-Qt6 (6.3.0, qtmultimedia qt5compat)	12m 13s
build-windows-vs-Qt6 (6.3.0, qtmultimedia qt5compat)	22m 8s
build-windows-vs-Qt6 (6.3.0, qtmultimedia qt5compat)	22m 8s
	4h 39m 22s

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