show: don't print nil targetfile

Author: Shiffted

xmake/plugins/show/info/target.lua

@@ -136,7 +136,10 @@ function _show_target(target)
     print("The information of target(%s):", target:name())
     cprint("    ${color.dump.string}at${clear}: %s", path.join(target:scriptdir(), "xmake.lua"))
     cprint("    ${color.dump.string}kind${clear}: %s", target:kind())
-    cprint("    ${color.dump.string}targetfile${clear}: %s", target:targetfile())
+    local targetfile = target:targetfile()
+    if targetfile then
+        cprint("    ${color.dump.string}targetfile${clear}: %s", targetfile)
+    end
     local deps = target:get("deps")
     if deps then
         cprint("    ${color.dump.string}deps${clear}:")