Restore ability to parse hours only with wxDateTime::ParseTime().

This was accidentally removed in r51059, but worked in 2.8 and so should
continue to work.

Also add a unit test to ensure that this doesn't get broken again in the
future.

Closes #15204.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73988 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/datetimefmt.cpp

@@ -2105,6 +2105,8 @@ wxDateTime::ParseTime(const wxString& time, wxString::const_iterator *end)
         "%H:%M:%S",     // could be the same or 24 hour one so try it too
         "%I:%M %p",     // 12hour with AM/PM but without seconds
         "%H:%M",        // and a possibly 24 hour version without seconds
+        "%I %p",        // just hour with AM/AM
+        "%H",           // just hour in 24 hour version
         "%X",           // possibly something from above or maybe something
                         // completely different -- try it last