fix String bug

length where returning something that is not 0 while buffer where NULL!?

Author: Links2004

cores/esp8266/WString.cpp

@@ -121,6 +121,7 @@ ICACHE_FLASH_ATTR String::~String() {
     if(buffer) {
         free(buffer);
     }
+    init();
 }
 
 // /*********************************************/
@@ -136,8 +137,7 @@ inline void String::init(void) {
 void ICACHE_FLASH_ATTR String::invalidate(void) {
     if(buffer)
         free(buffer);
-    buffer = NULL;
-    capacity = len = 0;
+    init();
 }
 
 unsigned char ICACHE_FLASH_ATTR String::reserve(unsigned int size) {

cores/esp8266/WString.h

@@ -76,7 +76,11 @@ class String {
         // invalid string (i.e., "if (s)" will be true afterwards)
         unsigned char reserve(unsigned int size);
         inline unsigned int length(void) const {
-            return len;
+            if(buffer) {
+                return len;
+            } else {
+                return 0;
+            }
         }
 
         // creates a copy of the assigned value.  if the value is null or