Format accepts @ modifier in the wrong position for aesthetic

Format accepts a control-string with a modifier in the wrong position for the aesthetic directive.

(format t "0123456789~%~@10A~%" "Ecce")

This should produce a format error.

ECL: 16.1.3 (git:UNKNOWN) "16.1.3" "UNKNOWN" "Linux" "4.19.0-9-amd64" "x86_64" (:WALKER :CDR-1 :CDR-5 :LINUX :FORMATTER :CDR-7 :ECL-WEAK-HASH :LITTLE-ENDIAN :ECL-READ-WRITE-LOCK :LONG-LONG :UINT64-T :UINT32-T :UINT16-T :RELATIVE-PACKAGE-NAMES :LONG-FLOAT :UNICODE :DFFI :CLOS-STREAMS :CMU-FORMAT :UNIX :ECL-PDE :DLOPEN :CLOS :THREADS :BOEHM-GC :ANSI-CL :COMMON-LISP :IEEE-FLOATING-POINT :CDR-14 :PREFIXED-API :FFI :X86_64 :COMMON :ECL)

The correct control-string does work.

(format t "0123456789~%~10@A~%" "Ecce")

outputs:

0123456789
      Ecce