Make serialize_excel registration conditional

Author: danielballan

tiled/serialization/sparse.py

@@ -37,6 +37,14 @@ def serialize_hdf5(sparse_arr, metadata):
     if modules_available("openpyxl"):
         from .table import serialize_excel
 
+        serialization_registry.register(
+            "sparse",
+            XLSX_MIME_TYPE,
+            lambda sparse_arr, metadata: serialize_excel(
+                to_dataframe(sparse_arr), metadata, preserve_index=False
+            ),
+        )
+
     # Support DataFrame formats by first converting to DataFrame.
     # naming columns like dim0, dim1, ..., dimN, data.
     def to_dataframe(sparse_arr):
@@ -82,13 +90,6 @@ def to_dataframe(sparse_arr):
             to_dataframe(sparse_arr), metadata, preserve_index=False
         ),
     )
-    serialization_registry.register(
-        "sparse",
-        XLSX_MIME_TYPE,
-        lambda sparse_arr, metadata: serialize_excel(
-            to_dataframe(sparse_arr), metadata, preserve_index=False
-        ),
-    )
     if modules_available("orjson"):
         import orjson