Revert "Just let oam_spr throw if we don't find a label"

This reverts commit 69156fa.

src/dotnes.tasks/Utilities/IL2NESWriter.cs

@@ -363,7 +363,14 @@ ushort GetAddress(string name)
             case nameof(scroll):
                 return 0x82FB;
             case nameof(oam_spr):
-                return Labels[nameof(oam_spr)];
+                if (Labels.TryGetValue(nameof(oam_spr), out var address))
+                {
+                    return address;
+                }
+                else
+                {
+                    return 0x0000;
+                }
             default:
                 throw new NotImplementedException($"{nameof(GetAddress)} for {name} is not implemented!");
         }