Backend: fix wrong UTXO-server exception thrown #2847

Job	Run time
windows--dotnet6-and-legacyFramework	8m 26s
macOS--dotnet6-and-mono	7m 30s
linux22-github--dotnet-and-newmono	4m 51s
linux22-github--dotnet-and-mono	4m 2s
macOS--dotnet6-only	4m 10s
windows--dotnet6-only	7m 39s
macOS--mono-only	6m 27s
windows--legacyFramework-only	7m 39s
linux20-github--dotnet-and-mono	4m 2s
linux20-github--dotnet-and-newmono	4m 37s
linux20-vanilla--stockmono-only	8m 10s
linux22-vanilla--newmono-only	8m 35s
linux22-vanilla--stockdotnet6-and-newmono	6m 38s
linux22-vanilla--stockdotnet6-and-stockmono	6m 33s
linux22-vanilla--stockdotnet6-only	6m 13s
linux22-vanilla--stockmono-only	7m 1s
linux20-vanilla--newmono-only	9m 40s
conventions	1m 45s
snap_pkg	5m 52s
	1h 59m 50s

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