Fix EditorFileSystem crash when fetching icons for unknown file types #40441

Job	Run time
📊 Static checks / Code style, file formatting, and docs	34s
🍏 iOS / Template (target=template_release)	1m 42s
🤖 Android / Editor (target=editor)	5m 5s
🍎 macOS / Editor (target=editor, tests=yes)	4m 12s
🤖 Android / Template arm32 (target=template_release, arch=arm32)	3m 46s
🐧 Linux / Editor w/ Mono (target=editor)	3m 44s
🍎 macOS / Template (target=template_release, tests=yes)	5m 6s
🤖 Android / Template arm64 (target=template_release, arch=arm64)	3m 34s
🐧 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)	17m 26s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	6m 27s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	6m 23s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	6m 17s
🐧 Linux / Template w/ Mono (target=template_release, tests=yes)	1m 13s
🌐 Web / Template w/o threads (target=template_release, threads=no)	7m 32s
🐧 Linux / Minimal template (target=template_release, tests=yes, everything disabled)	57s
🏁 Windows / Editor (target=editor, tests=yes)	11m 22s
🏁 Windows / Editor w/ clang-cl (target=editor, tests=yes, use_llvm=yes)	6m 30s
🏁 Windows / Template (target=template_release, tests=yes)	8m 35s
🪲 Godot CPP / Build and test Godot CPP	8m 34s
	1h 48m 59s

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