patch 8.2.1150: ml_get error when using Python

Problem:    ml_get error when using Python. (Yegappan Lakshmanan)
Solution:   Check the line number is not out of range.  Call "Check" with
            "fromObj" instead of "from".
diff --git a/src/if_py_both.h b/src/if_py_both.h
index c7df93b..5bd6a0e 100644
--- a/src/if_py_both.h
+++ b/src/if_py_both.h
@@ -3374,7 +3374,7 @@
     char_u	*stringval;
     PyObject	*todecref;
 
-    if (self->Check(self->from))
+    if (self->Check(self->fromObj))
 	return NULL;
 
     if (!(key = StringToChars(keyObject, &todecref)))
@@ -3565,7 +3565,7 @@
     int		ret = 0;
     PyObject	*todecref;
 
-    if (self->Check(self->from))
+    if (self->Check(self->fromObj))
 	return -1;
 
     if (!(key = StringToChars(keyObject, &todecref)))
@@ -4334,10 +4334,15 @@
 
     for (i = 0; i < n; ++i)
     {
-	PyObject	*string = LineToString(
-		(char *)ml_get_buf(buf, (linenr_T)(lo+i), FALSE));
+	linenr_T	lnum = (linenr_T)(lo + i);
+	char		*text;
+	PyObject	*string;
 
-	// Error check - was the Python string creation OK?
+	if (lnum > buf->b_ml.ml_line_count)
+	    text = "";
+	else
+	    text = (char *)ml_get_buf(buf, lnum, FALSE);
+	string = LineToString(text);
 	if (string == NULL)
 	{
 	    Py_DECREF(list);