fix unnecessary IRQ clear

src/helpers/radiolib/CustomSX1262.h

@@ -117,6 +117,12 @@ class CustomSX1262 : public SX1262 {
         _headerSeen = false;
         return false;
       }
+      if (!header && _headerSeen) {
+        // something cleared the header flag, reset our state.
+        _activityAt = 0; _headerSeen = false;
+        return false;
+      }
+
       if (header) {
         if (!_headerSeen) { _headerSeen = true; _activityAt = now; };
         if (now - _activityAt > _maxPayloadMillis) {