patch 8.2.0743: can move to another buffer from a terminal in popup window

Problem:    Can move to another buffer from a terminal in popup window.
Solution:   Do not allow "gf" or editing a file. (closes #6072)
diff --git a/src/normal.c b/src/normal.c
index 7dd74a4..690bb00 100644
--- a/src/normal.c
+++ b/src/normal.c
@@ -4169,6 +4169,10 @@
 	clearop(cap->oap);
 	return;
     }
+#ifdef FEAT_PROP_POPUP
+    if (ERROR_IF_TERM_POPUP_WINDOW)
+	return;
+#endif
 
     ptr = grab_file_name(cap->count1, &lnum);