skip empty description

Don't print the description of a command as a subtitle
when generating a manpage if the description is empty.
This commit addresses #9430

Signed-off-by: Harumi Kuno <harumi.kuno@hpe.com>

sphinx/writers/manpage.py

@@ -113,7 +113,8 @@ def __init__(self, document: nodes.document, builder: Builder) -> None:
     def header(self) -> str:
         tmpl = (".TH \"%(title_upper)s\" \"%(manual_section)s\""
                 " \"%(date)s\" \"%(version)s\" \"%(manual_group)s\"\n"
-                ".SH NAME\n"
+                ".SH NAME\n")
+        if self._docinfo['subtitle']:
                 "%(title)s \\- %(subtitle)s\n")
         return tmpl % self._docinfo