Fix editor crash when invalid global class script path #153

Job	Run time
📊 Static checks / Code style, file formatting, and docs	1m 11s
🍏 iOS / Template (target=template_release)	9m 42s
🤖 Android / Template (target=template_release)	30m 16s
🍎 macOS / Editor (target=editor, tests=yes)	27m 41s
🍎 macOS / Template (target=template_release)	18m 35s
🐧 Linux / Editor w/ Mono (target=editor)	39m 52s
🐧 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)	46m 8s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	24m 35s
🏁 Windows / Editor (target=editor, tests=yes)	48m 13s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	34m 28s
🌐 Web / Template w/o threads (target=template_release, threads=no)	24m 19s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	30m 49s
🏁 Windows / Template (target=template_release)	35m 0s
🐧 Linux / Template w/ Mono (target=template_release)	24m 52s
🐧 Linux / Minimal template (target=template_release, everything disabled)	14m 32s
🪲 Godot CPP / Build and test Godot CPP	7m 37s
	6h 57m 50s

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