Fix layout input field in (Gridfinity-)Traylayout

This was broken with cc78633 which now
requires \n in the default value to get a text area (instead of layout as
the name)

Thanks to Michael Moorhouse <https://github.com/mjmoorhouse> for
reporting!

Resolves: #635

boxes/generators/gridfinitytraylayout.py

@@ -37,7 +37,7 @@ def __init__(self) -> None:
         self.argparser.add_argument("--countx", type=int, default=5, help="split x into this many grid sections.  0 means same as --nx")
         self.argparser.add_argument("--county", type=int, default=3, help="split y into this many grid sections.  0 means same as --ny")
         self.argparser.add_argument("--margin", type=float, default=0.75, help="Leave this much total margin on the outside, in mm")
-        self.argparser.add_argument("--layout", type=str, help="You can hand edit this before generating", default="");
+        self.argparser.add_argument("--layout", type=str, help="You can hand edit this before generating", default="\n");
 
     def generate_layout(self):
         layout = ''

boxes/generators/traylayout.py

@@ -104,7 +104,7 @@ def __init__(self) -> None:
         self.buildArgParser("h", "hi", "outside", "sx", "sy")
         if self.UI == "web":
             self.argparser.add_argument(
-                "--layout", action="store", type=str, default="")
+                "--layout", action="store", type=str, default="\n")
         else:
             self.argparser.add_argument(
                 "--input", action="store", type=argparse.FileType('r'),