upgrade: fix output when no packages to upgrade.

When upgrading, if the only package to upgrade is a
pinned package, the output looked like that:
	==> Upgrading 0 packages, with result:

	==> Not upgrading 1 pinned package:
	<<package_name & version>>

The blank line is not beautiful. This commit fixes
the output and replaces with:
	==> No packages to upgrade
	==> Not upgrading 1 pinned package:
	<<package_name & version>>

Closes Homebrew/homebrew#26157.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Library/Homebrew/cmd/upgrade.rb

@@ -34,8 +34,12 @@ module Homebrew extend self
       outdated -= pinned
     end
 
-    oh1 "Upgrading #{outdated.length} outdated package#{outdated.length.plural_s}, with result:"
-    puts outdated.map{ |f| "#{f.name} #{f.version}" } * ", "
+    unless outdated.empty?
+      oh1 "Upgrading #{outdated.length} outdated package#{outdated.length.plural_s}, with result:"
+      puts outdated.map{ |f| "#{f.name} #{f.version}" } * ", "
+    else
+      oh1 "No packages to upgrade"
+    end
 
     unless upgrade_pinned? || pinned.empty?
       oh1 "Not upgrading #{pinned.length} pinned package#{pinned.length.plural_s}:"