patch 8.1.0975: using STRNCPY() wrongly. Warning for uninitialized variable

Problem:    Using STRNCPY() wrongly. Warning for uninitialized variable.
Solution:   Use mch_memmove(). Initialize variable. (Yasuhiro Matsumoto,
            closes #3979)
diff --git a/src/screen.c b/src/screen.c
index 4973b51..aade363 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -2547,10 +2547,10 @@
 	{
 #ifdef FEAT_RIGHTLEFT
 	    if (wp->w_p_rl)
-		STRNCPY(current_ScreenLine, text, len);
+		mch_memmove(current_ScreenLine, text, len);
 	    else
 #endif
-		STRNCPY(current_ScreenLine + col, text, len);
+		mch_memmove(current_ScreenLine + col, text, len);
 	    col += len;
 	}
     }
@@ -3396,7 +3396,7 @@
 	{
 	    if (lnum == curwin->w_cursor.lnum)
 		getvcol(curwin, &(curwin->w_cursor),
-						 (colnr_T *)&fromcol, NULL, NULL);
+					      (colnr_T *)&fromcol, NULL, NULL);
 	    else
 		fromcol = 0;
 	    if (lnum == curwin->w_cursor.lnum + search_match_lines)