fix UB with the function iscntrl()

From commit 6818e07291f3b2913e687c8ec3d3fe4711724050 by NRK, thanks

1 files changed, 1 insertions, 1 deletions

diff --git a/dmenu.c b/dmenu.c
index 085dc29..839f6cc 100644
--- a/dmenu.c
+++ b/dmenu.c
@@ -415,7 +415,7 @@ keypress(XKeyEvent *ev)
         switch(ksym) {
         default:
 insert:
-                if (!iscntrl(*buf))
+                if (!iscntrl((unsigned char)*buf))
                         insert(buf, len);
                 break;
         case XK_Delete: