imaadp32: Refuse unknown destination format.

ADPCM_FormatSuggest must report NOTPOSSIBLE if the destination format
is not supported.

dlls/imaadp32.acm/imaadp32.c

@@ -697,8 +697,7 @@ static	LRESULT	ADPCM_FormatSuggest(PACMDRVFORMATSUGGEST adfs)
         if (ADPCM_GetFormatIndex(adfs->pwfxDst) == 0xFFFFFFFF) return ACMERR_NOTPOSSIBLE;
         break;
     default:
-        FIXME("\n");
-        break;
+        return ACMERR_NOTPOSSIBLE;
     }
 
     return MMSYSERR_NOERROR;