fix non-unwrapped string

Sources/String+Misc.swift

@@ -41,7 +41,7 @@ extension String {
     
     public static func fromUInt8(array: [UInt8]) -> String {
         #if os(Linux)
-            return String(data: NSData(bytes: array, length: array.count), encoding: NSUTF8StringEncoding)
+            return String(data: NSData(bytes: array, length: array.count), encoding: NSUTF8StringEncoding) ?? ""
         #else
             if let s = String(data: NSData(bytes: array, length: array.count), encoding: NSUTF8StringEncoding) {
                 return s