Set data_dirs closer to first use

Reducing the scope of variables reduces possible dependencies between
parts of this function, and will make it easier to extract this section
into its own function.

src/pip/_internal/operations/install/wheel.py

@@ -366,10 +366,6 @@ def install_unpacked_wheel(
     else:
         lib_dir = scheme.platlib
 
-    # Zip file path separators must be /
-    subdirs = set(p.split("/", 1)[0] for p in wheel_zip.namelist())
-    data_dirs = [s for s in subdirs if s.endswith('.data')]
-
     # Record details of the files moved
     #   installed = files copied from the wheel to the destination
     #   changed = files changed while installing (scripts #! line typically)
@@ -486,6 +482,10 @@ def is_entrypoint_wrapper(name):
         # Ignore setuptools-generated scripts
         return (matchname in console or matchname in gui)
 
+    # Zip file path separators must be /
+    subdirs = set(p.split("/", 1)[0] for p in wheel_zip.namelist())
+    data_dirs = [s for s in subdirs if s.endswith('.data')]
+
     for datadir in data_dirs:
         fixer = None
         filter = None