add "index" keyword to ascii reader to use row number; part of #135

src/gui_qt/io/asciireader.py

@@ -179,9 +179,13 @@ class QAsciiReader(QtWidgets.QDialog, Ui_ascii_reader):
 
     def apply(self):
         # default row for x is the first row, it will be superseded if an integer number is given.
-        try:
-            x = int(self.x_lineedit.text())-1
-        except ValueError:
+        x = self.x_lineedit.text()
+        if x:
+            try:
+                x = int(x)-1
+            except ValueError:
+                pass
+        else:
             x = None
 
         try: