storage/udisks2: move empty string check out of the fallback block in MapUTF8()

src/storage/plugins/UdisksStorage.cxx

@@ -331,16 +331,18 @@ UdisksStorage::MapUTF8(const char *uri_utf8) const noexcept
 {
 	assert(uri_utf8 != nullptr);
 
+	if (StringIsEmpty(uri_utf8))
+		/* kludge for a special case: return the "udisks://"
+		   URI if the parameter is an empty string to fix the
+		   mount URIs in the state file */
+		return base_uri;
+
 	try {
 		const_cast<UdisksStorage *>(this)->MountWait();
 
 		return mounted_storage->MapUTF8(uri_utf8);
 	} catch (...) {
 		/* fallback - not usable but the best we can do */
-
-		if (StringIsEmpty(uri_utf8))
-			return base_uri;
-
 		return PathTraitsUTF8::Build(base_uri.c_str(), uri_utf8);
 	}
 }