add error msg when oappend buffer is used up

wled00/const.h

@@ -351,6 +351,7 @@
 #define ERR_LOW_MEM     33  // WLEDMM: low memory (RAM)
 #define ERR_LOW_SEG_MEM 34  // WLEDMM: low memory (segment data RAM)
 #define ERR_LOW_WS_MEM  35  // WLEDMM: low memory (ws)
+#define ERR_LOW_AJAX_MEM  36 // WLEDMM: low memory (oappend)
 
 // Timer mode types
 #define NL_MODE_SET               0            //After nightlight time elapsed, set to target brightness

wled00/util.cpp

@@ -155,6 +155,7 @@ bool oappend(const char* txt)
       USER_PRINTF("%2u bytes \t\"", len /*1 + olen + len - SETTINGS_STACK_BUF_SIZE*/);
       USER_PRINT(txt);
       USER_PRINTLN(F("\""));
+      errorFlag = ERR_LOW_AJAX_MEM;
 	  }
     return false;        // buffer full
   }