fix: don't assume that any configurations are active

cibuildwheel/macos.py

@@ -276,6 +276,7 @@ def build(options: Options, tmp_path: Path) -> None:
     )
 
     try:
+        if len(python_configurations) > 0:
             before_all_options_identifier = python_configurations[0].identifier
             before_all_options = options.build_options(before_all_options_identifier)
 

cibuildwheel/windows.py

@@ -235,6 +235,7 @@ def build(options: Options, tmp_path: Path) -> None:
     )
 
     try:
+        if len(python_configurations) > 0:
             before_all_options_identifier = python_configurations[0].identifier
             before_all_options = options.build_options(before_all_options_identifier)