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)

src/screen.c

@@ -2981,6 +2981,16 @@ lineinvalid(unsigned off, int width)
     (void)vim_memset(ScreenAttrs + off, -1, (size_t)width * sizeof(sattr_T));
 }
 
+/*
+ * 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".
  */