uucore: simplify fallback when splice failed #12732

Job	Run time
L10n/Embedded Locale Regression Test	1m 34s
L10n/Multi-call Binary Install Test (ubuntu-latest, feat_os_unix)	4m 30s
L10n/Locale Support Verification	7m 59s
L10n/Installation Test (Make & Cargo) (macos-latest, feat_os_unix)	12m 0s
L10n/Installation Test (Make & Cargo) (ubuntu-latest, feat_os_unix)	7m 14s
L10n/French Integration Test	1m 57s
L10n/Fluent Syntax Check	15s
L10n/Multi-call Binary Install Test (macos-latest, feat_os_unix)	4m 21s
L10n/Locale Embedding - Multicall Binary	2m 50s
L10n/Clap Error Localization Test	1m 35s
L10n/Locale Embedding - Cat Utility	44s
L10n/Locale Embedding - Ls Utility	1m 15s
L10n/Locale Embedding - Cargo Install	58s
L10n/Build and Test (windows-latest, feat_os_windows)	8m 13s
L10n/Build and Test (ubuntu-latest, feat_os_unix)	3m 16s
L10n/Build and Test (macos-latest, feat_os_unix)	5m 23s
	1h 4m 4s

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