Better oappend shim on ESP8266

Detect IRAM pointers if we can't be sure.

wled00/fcn_declare.h

@@ -324,6 +324,10 @@ class Usermod {
   protected:
     // Shim for oappend(), which used to exist in utils.cpp
     template<typename T> static inline void oappend(const T& t) { oappend_shim->print(t); };
+#ifdef ESP8266
+    // Handle print(PSTR()) without crashing by detecting PROGMEM strings
+    static void oappend(const char* c) { if ((intptr_t) c >= 0x40000000) oappend_shim->print(FPSTR(c)); else oappend_shim->print(c); };
+#endif
 };
 
 class UsermodManager {