csi: only respond to Primary DA when Ps == 0

CHANGELOG.md

@@ -68,6 +68,7 @@
   (https://codeberg.org/dnkl/foot/issues/151).
 * Crash after either resizing a window or changing the font size if
   there were sixels present in the scrollback while doing so.
+* _Send Device Attributes_ to only send a response if `Ps == 0`.
 
 
 ### Security

csi.c

@@ -660,6 +660,11 @@ csi_dispatch(struct terminal *term, uint8_t final)
             break;
 
         case 'c': {
+            if (vt_param_get(term, 0, 0) != 0) {
+                UNHANDLED();
+                break;
+            }
+
             /* Send Device Attributes (Primary DA) */
 
             /*