fix double path delimiter (#18923)

A cosmetic fix. It removes a double delimiter at the end of a path in
`games.yml` when using `VFS games` path.

Utilities/StrFmt.cpp

@@ -921,6 +921,13 @@ std::string_view fmt::trim_front_sv(std::string_view source, std::string_view va
 void fmt::trim_back(std::string& source, std::string_view values)
 {
 	const usz index = source.find_last_not_of(values);
+
+	if (index == source.npos)
+	{
+		source.clear();
+		return;
+	}
+
 	source.resize(index + 1);
 }