Clean windows display after resizing

Some times the size after a resizing is not an exact multiply of a number of
characters, so redrawn the screen using the lines and columns of the neww
size can cause that some old graphics keep in the screen. Solution is clean
all the windows with the background color.
---
 st.c |    3 +++
 1 file changed, 3 insertions(+)

st.c

@@ -1839,6 +1839,9 @@ void
 xresize(int col, int row) {
 	xw.w = MAX(1, 2*BORDER + col * xw.cw);
 	xw.h = MAX(1, 2*BORDER + row * xw.ch);
+	XFillRectangle(xw.dpy, xw.buf, dc.gc, 0, 0,
+		       DisplayWidth(xw.dpy, xw.scr),
+		       DisplayHeight(xw.dpy, xw.scr));
 }
 
 void