Only access BuiltInLibrariesFolders if initialized

Author: facchinm

src/arduino.cc/builder/tools_loader.go

@@ -52,7 +52,10 @@ func (s *ToolsLoader) Run(ctx *types.Context) error {
 		if err != nil {
 			return i18n.WrapError(err)
 		}
-		builtinHardwareFolder, err := filepath.Abs(filepath.Join(ctx.BuiltInLibrariesFolders[0], ".."))
+		builtinHardwareFolder := ""
+		if len(ctx.BuiltInLibrariesFolders) > 0 {
+			builtinHardwareFolder, err = filepath.Abs(filepath.Join(ctx.BuiltInLibrariesFolders[0], ".."))
+		}
 
 		if builtinToolsVersionsFile != constants.EMPTY_STRING && !strings.Contains(builtinToolsVersionsFile, builtinHardwareFolder) {
 			ctx.GetLogger().Println(constants.LOG_LEVEL_WARN, constants.MSG_IGNORED_BUILTIN_TOOLS_TXT, builtinToolsVersionsFile)