patch 8.2.2244: crash when making the window width negative

Problem:    Crash when making the window width of the not-current window
            negative.
Solution:   Make sure the window width is not negative. (closes #7568)
diff --git a/src/window.c b/src/window.c
index 1cf795f..bea4f39 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5687,6 +5687,8 @@
 	if (width == 0)
 	    width = 1;
     }
+    else if (width < 0)
+	width = 0;
 
     frame_setwidth(wp->w_frame, width + wp->w_vsep_width);