patch 8.2.4711: when 'insermode' is set :edit from <Cmd> mapping misbehaves

Problem:    When 'insermode' is set :edit from <Cmd> mapping misbehaves.
Solution:   Don't set "need_start_insertmode" when already in Insert mode.
            (closes #10116)
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index 8cdac4b..50829be 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -3182,7 +3182,7 @@
 	redraw_curbuf_later(NOT_VALID);	// redraw this buffer later
     }
 
-    if (p_im)
+    if (p_im && (State & INSERT) == 0)
 	need_start_insertmode = TRUE;
 
 #ifdef FEAT_AUTOCHDIR