patch 8.1.0623: iterating through window frames is repeated

Problem:    Iterating through window frames is repeated.
Solution:   Define FOR_ALL_FRAMES. (Yegappan Lakshmanan)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 466e77e..d3246f4 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -11688,7 +11688,7 @@
 {
     frame_T	*frc;
 
-    for (frc = fr; frc != NULL; frc = frc->fr_next)
+    FOR_ALL_FRAMES(frc, fr)
 	if (ses_do_frame(frc))
 	    break;
     return frc;
@@ -11705,7 +11705,7 @@
 
     if (fr->fr_layout == FR_LEAF)
 	return ses_do_win(fr->fr_win);
-    for (frc = fr->fr_child; frc != NULL; frc = frc->fr_next)
+    FOR_ALL_FRAMES(frc, fr->fr_child)
 	if (ses_do_frame(frc))
 	    return TRUE;
     return FALSE;