editor: Fix selection anchor on text deletion

When text is deleted adjust selection anchor.
diff --git a/clients/editor.c b/clients/editor.c
index 5c75ac1..af1623f 100644
--- a/clients/editor.c
+++ b/clients/editor.c
@@ -591,6 +591,8 @@
 	if (entry->cursor > index)
 		entry->cursor -= length;
 
+	entry->anchor = entry->cursor;
+
 	entry->text[index] = '\0';
 	strcat(entry->text, entry->text + index + length);