transactions (qt): fix opening raw bytes files

(both when trying to "load tx from file", and "load tx from text" > "browse file")

electrum/gui/qt/main_window.py

@@ -2755,7 +2755,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
         if not fileName:
             return
         try:
-            with open(fileName, "r") as f:
+            with open(fileName, "rb") as f:
                 file_content = f.read()  # type: Union[str, bytes]
         except (ValueError, IOError, os.error) as reason:
             self.show_critical(_("Electrum was unable to open your transaction file") + "\n" + str(reason),

electrum/gui/qt/qrtextedit.py

@@ -47,8 +47,13 @@ class ScanQRTextEdit(ButtonsTextEdit, MessageBoxMixin):
         if not fileName:
             return
         try:
-            with open(fileName, "r") as f:
+            try:
-                data = f.read()
+                with open(fileName, "r") as f:
+                    data = f.read()
+            except UnicodeError as e:
+                with open(fileName, "rb") as f:
+                    data = f.read()
+                data = data.hex()
         except BaseException as e:
             self.show_error(_('Error opening file') + ':\n' + repr(e))
         else: