run openInputstream in IO context

app/src/main/java/org/wntr/mdeditor/MainActivity.kt

@@ -991,17 +991,21 @@ class MainActivity : AppCompatActivity() {
             })
         }
         try {
-            contentResolver.openInputStream(uri)?.use { inputStream ->
-                BufferedReader(InputStreamReader(inputStream)).use { reader ->
-                    var i = ""
-                    if (reader.ready()) {
-                        i = reader.readLine()
-                        var line: String? = ""
-                        while (line != null) {
-                            i += line + '\n'
-                            line = reader.readLine()
+            CoroutineScope(Dispatchers.Main).launch {
+                withContext(Dispatchers.IO) {
+                    contentResolver.openInputStream(uri)?.use { inputStream ->
+                        BufferedReader(InputStreamReader(inputStream)).use { reader ->
+                            var i = ""
+                            if (reader.ready()) {
+                                i = reader.readLine()
+                                var line: String? = ""
+                                while (line != null) {
+                                    i += line + '\n'
+                                    line = reader.readLine()
+                                }
+                                mdeValue = metaData.extractMetadataFromMarkdown(i)
+                            }
                         }
-                        mdeValue = metaData.extractMetadataFromMarkdown(i)
                     }
                 }
             }