test file presence to avoid error

LeStorage/MicroStorage.swift

@@ -19,13 +19,17 @@ class MicroStorage<T : MicroStorable> {
     init() {
         var instance: T? = nil
         do {
-            let jsonString = try FileUtils.readDocumentFile(fileName: T.fileName)
-            if let decoded: T = try jsonString.decode() {
-                instance = decoded
+            let url = try FileUtils.directoryURLForFileName(T.fileName)
+            if FileManager.default.fileExists(atPath: url.absoluteString) {
+                let jsonString = try FileUtils.readDocumentFile(fileName: T.fileName)
+                if let decoded: T = try jsonString.decode() {
+                    instance = decoded
+                }
             }
         } catch {
             Logger.error(error)
         }
+        
         self.item = instance ?? T()
     }