EditorResourcePreview: Let loads complete after exit requested #899

Job	Run time
📊 Static checks / Code style, file formatting, and docs	1m 19s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	26m 13s
🤖 Android / Editor (target=editor)	24m 22s
🌐 Web / Template w/o threads (target=template_release, threads=no)	25m 52s
🤖 Android / Template arm32 (target=template_release, arch=arm32)	16m 41s
🍎 macOS / Editor (target=editor, tests=yes)	28m 34s
🤖 Android / Template arm64 (target=template_release, arch=arm64)	16m 54s
🍎 macOS / Template (target=template_release)	19m 37s
🏁 Windows / Editor (target=editor, tests=yes)	49m 20s
🏁 Windows / Template (target=template_release)	35m 31s
🍏 iOS / Template (target=template_release)	9m 14s
🐧 Linux / Editor w/ Mono (target=editor)	39m 46s
🐧 Linux / Editor with doubles and GCC sanitizers (target=editor, tests=yes, dev_build=yes, scu_build=yes, precision=double, use_asan=yes, use_ubsan=yes, linker=gold)	44m 39s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	36m 17s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	31m 30s
🐧 Linux / Template w/ Mono (target=template_release)	28m 7s
🐧 Linux / Minimal template (target=template_release, everything disabled)	14m 40s
🪲 Godot CPP / Build and test Godot CPP	8m 8s
	7h 36m 44s

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