Merge pull request esp8266#1735 from Links2004/master

fix umm_malloc null ptr.

Author: igrr

cores/esp8266/umm_malloc/umm_malloc.c

@@ -971,6 +971,10 @@ void ICACHE_FLASH_ATTR *umm_info( void *ptr, int force ) {
 
   unsigned short int blockNo = 0;
 
+  if (umm_heap == NULL) {
+      umm_init();
+  }
+
   /* Protect the critical section... */
   UMM_CRITICAL_ENTRY();