patch 8.2.1164: text cleared by checking terminal properties not redrawn

Problem:    Text cleared by checking terminal properties not redrawn. (Alexey
            Radkov)
Solution:   Mark the screen characters as invalid. (closes #6422)
diff --git a/src/screen.c b/src/screen.c
index 01d6257..0d65b4b 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -2982,6 +2982,16 @@
 }
 
 /*
+ * To be called when characters were sent to the terminal directly, outputting
+ * test on "screen_lnum".
+ */
+    void
+line_was_clobbered(int screen_lnum)
+{
+    lineinvalid(LineOffset[screen_lnum], (int)Columns);
+}
+
+/*
  * Copy part of a Screenline for vertically split window "wp".
  */
     static void