oappend robustness improvement

obuf is reset to nullptr in some cases

Author: softhack007

wled00/util.cpp

@@ -148,11 +148,14 @@ bool oappendi(int i)
 bool oappend(const char* txt)
 {
   uint16_t len = strlen(txt);
-  if (olen + len >= SETTINGS_STACK_BUF_SIZE) {
-    USER_PRINT(F("oappend() error: buffer full. Increase SETTINGS_STACK_BUF_SIZE for "));
-    USER_PRINTF("%2u bytes \t\"", len /*1 + olen + len - SETTINGS_STACK_BUF_SIZE*/);
-    USER_PRINT(txt);
-    USER_PRINTLN(F("\""));
+  if ((obuf == nullptr) || (olen + len >= SETTINGS_STACK_BUF_SIZE)) { // sanity checks
+	if (obuf == nullptr) { USER_PRINTLN(F("oappend() error: obuf == nullptr."));
+	} else {
+	  USER_PRINT(F("oappend() error: buffer full. Increase SETTINGS_STACK_BUF_SIZE for "));
+      USER_PRINTF("%2u bytes \t\"", len /*1 + olen + len - SETTINGS_STACK_BUF_SIZE*/);
+      USER_PRINT(txt);
+      USER_PRINTLN(F("\""));
+	}
     return false;        // buffer full
   }
   strcpy(obuf + olen, txt);