Get biome list: Downgrade missing biome message to infostream

It is harmless for a biome listed in an ore or decoration registration
to be missing.
Now that we are registering certain biomes or not based on options
(such as floatland biomes), the biome lists in ore and decoration
registrations trigger these error messages, avoiding these error
messages would need a large amount of duplication of ore and decoration
registrations.

src/script/lua_api/l_mapgen.cpp

@@ -419,7 +419,7 @@ size_t get_biome_list(lua_State *L, int index,
 	if (is_single) {
 		Biome *biome = get_or_load_biome(L, index, biomemgr);
 		if (!biome) {
-			errorstream << "get_biome_list: failed to get biome '"
+			infostream << "get_biome_list: failed to get biome '"
 				<< (lua_isstring(L, index) ? lua_tostring(L, index) : "")
 				<< "'." << std::endl;
 			return 1;
@@ -438,7 +438,7 @@ size_t get_biome_list(lua_State *L, int index,
 		Biome *biome = get_or_load_biome(L, -1, biomemgr);
 		if (!biome) {
 			fail_count++;
-			errorstream << "get_biome_list: failed to get biome '"
+			infostream << "get_biome_list: failed to get biome '"
 				<< (lua_isstring(L, -1) ? lua_tostring(L, -1) : "")
 				<< "'" << std::endl;
 			continue;
@@ -927,7 +927,7 @@ int ModApiMapgen::l_register_decoration(lua_State *L)
 	//// Get biomes associated with this decoration (if any)
 	lua_getfield(L, index, "biomes");
 	if (get_biome_list(L, -1, biomemgr, &deco->biomes))
-		errorstream << "register_decoration: couldn't get all biomes " << std::endl;
+		infostream << "register_decoration: couldn't get all biomes " << std::endl;
 	lua_pop(L, 1);
 
 	//// Get node name(s) to 'spawn by'
@@ -1092,7 +1092,7 @@ int ModApiMapgen::l_register_ore(lua_State *L)
 	//// Get biomes associated with this decoration (if any)
 	lua_getfield(L, index, "biomes");
 	if (get_biome_list(L, -1, bmgr, &ore->biomes))
-		errorstream << "register_ore: couldn't get all biomes " << std::endl;
+		infostream << "register_ore: couldn't get all biomes " << std::endl;
 	lua_pop(L, 1);
 
 	//// Get noise parameters if needed