patch 8.1.1032: warnings from clang static analyzer

Problem:    Warnings from clang static analyzer. (Yegappan Lakshmanan)
Solution:   Fix relevant warnings.
diff --git a/src/screen.c b/src/screen.c
index 111c77d..c01a74c 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -4900,7 +4900,7 @@
 		    else
 		    {
 			char_u *p;
-			int	len = n_extra;
+			int	len;
 			int	i;
 			int	saved_nextra = n_extra;
 
@@ -5505,8 +5505,8 @@
 	    if (vcol < v + col - win_col_off(wp))
 		vcol = v + col - win_col_off(wp);
 #ifdef FEAT_CONCEAL
-	    /* Get rid of the boguscols now, we want to draw until the right
-	     * edge for 'cursorcolumn'. */
+	    // Get rid of the boguscols now, we want to draw until the right
+	    // edge for 'cursorcolumn'.
 	    col -= boguscols;
 	    boguscols = 0;
 #endif
@@ -10466,7 +10466,6 @@
 
 	attr = attr_nosel;
 	tabcount = 0;
-	scol = 0;
 	for (tp = first_tabpage; tp != NULL && col < Columns - 4;
 							     tp = tp->tp_next)
 	{
@@ -10799,7 +10798,7 @@
     int		o;
     int		this_ru_col;
     int		off = 0;
-    int		width = Columns;
+    int		width;
 
     /* If 'ruler' off or redrawing disabled, don't do anything */
     if (!p_ru)