close streams after copying

mirai-core/src/jvmMain/kotlin/net/mamoe/mirai/utils/PlatformUtilsJvm.kt

@@ -24,12 +24,14 @@ actual fun md5(byteArray: ByteArray): ByteArray = MessageDigest.getInstance("MD5
 fun InputStream.md5(): ByteArray = this.use {
     val digest = MessageDigest.getInstance("md5")
     digest.reset()
-    this.use {
-        it.copyTo(object : OutputStream() {
+    this.use { input ->
+        object : OutputStream() {
             override fun write(b: Int) {
                 digest.update(b.toByte())
             }
-        })
+        }.use { output ->
+            input.copyTo(output)
+        }
     }
     return digest.digest()
 }