import: pypi: Fix null at home-page.

Reported in #73314: PyPI importer gives null at home-page for some
packages.

* guix/import/pypi.scm (<project-info>): [home-page]: Apply
NON-EMPTY-STRING-OR-FALSE to make it consistence with similar fields,
covering the case when PyPI's JSON file metadata file does not have the
information.

Change-Id: I501582988cf58b00bd201c12ad47e9b095988fae
Reported-by: Evgeny Pisemsky <mail@pisemsky.site>
Reviewed-by: Simon Tournier <zimon.toutoune@gmail.com>
Signed-off-by: Sharlatan Hellseher <sharlatanus@gmail.com>

guix/import/pypi.scm

@@ -116,8 +116,8 @@
   (license      project-info-license)             ;string
   (download-url project-info-download-url         ;string | #f
                 "download_url" non-empty-string-or-false)
-  (home-page    project-info-home-page            ;string
-                "home_page")
+  (home-page    project-info-home-page            ;string | #f
+                "home_page" non-empty-string-or-false)
   (url          project-info-url "project_url")   ;string
   (release-url  project-info-release-url "release_url") ;string
   (version      project-info-version))            ;string

guix/packages.scm

@@ -651,7 +651,7 @@ Texinfo.  Otherwise, return the string."
                (sanitize validate-texinfo))       ; one or two paragraphs
   (license package-license                        ; (list of) <license>
            (sanitize validate-license))
-  (home-page package-home-page)                   ; string
+  (home-page package-home-page)                   ; string | #f
   (supported-systems package-supported-systems    ; list of strings
                      (default %supported-systems))