mcl_mapgen_core: Make mcl_farming an optional dependency.

mcl_farming was previously an undeclared dependency of mcl_mapgen_core.
Now it is both optional and declared.

mods/MAPGEN/mcl_mapgen_core/init.lua

@@ -843,6 +843,7 @@ local function register_mgv6_decorations()
 		})
 	end
 
+	if minetest.get_modpath("mcl_farming") then
 		-- Pumpkin
 		minetest.register_decoration({
 			deco_type = "simple",
@@ -883,6 +884,7 @@ local function register_mgv6_decorations()
 			y_max = 40,
 			decoration = "mcl_farming:melon",
 		})
+	end
 
 	-- Tall grass
 	if minetest.get_modpath("mcl_flowers") then

mods/MAPGEN/mcl_mapgen_core/mod.conf

@@ -2,4 +2,4 @@ name = mcl_mapgen_core
 author = Wuzzy
 description = The core of the MCL2 mapgen
 depends = mcl_init, mcl_core, biomeinfo, mcl_worlds
-optional_depends = mclx_core, mcl_cocoas, mcl_sponges, mcl_ocean, mcl_stairs, mcl_monster_eggs, mcl_structures, mcl_flowers
+optional_depends = mclx_core, mcl_cocoas, mcl_sponges, mcl_ocean, mcl_stairs, mcl_monster_eggs, mcl_structures, mcl_flowers, mcl_farming