AP_InternalError: make constraining NaNs an internal error

libraries/AP_InternalError/AP_InternalError.h

@@ -43,6 +43,7 @@ public:
         logger_bad_current_block    = (1U <<  7),
         logger_blockcount_mismatch  = (1U <<  8),
         logger_dequeue_failure      = (1U <<  9),
+        constraining_nan            = (1U << 10),
     };
 
     void error(const AP_InternalError::error_t error);