Panel_AMOLED: do not keep a framebuffer object whose init failed

[ainyan03]

Summary

Panel_AMOLED::initPanelFb() assigned _panel_fb before calling init(). When the PSRAM frame buffer allocation failed, the object stayed behind without a buffer, so:

• the next initPanelFb() call returned true immediately without allocating anything, and
• display() was routed through a frame buffer that does not exist.

A caller that adopts that panel after the "successful" retry (the CO5300-based board setup does exactly this) dereferences a null line buffer. The object is now created locally with std::nothrow (exceptions are disabled on the ESP32 targets, so a throwing new that fails would terminate instead of letting the caller fall back to direct drawing) and published to _panel_fb only after init() succeeds; on any failure it is released and the method returns false as documented.

Verified

Test firmware on an ESP32-S3 board with a 468x468 CO5300 panel: exhaust PSRAM before init so the frame buffer allocation fails, free it, then call initPanelFb() again and adopt the returned panel.

	first call (no PSRAM)	retry after freeing PSRAM	drawing through the adopted panel
before	returns true with a stale object	returns true, PSRAM usage unchanged (0 bytes)	LoadProhibited at address 0, reset loop
after	returns false, getPanelFb() is null	returns true, 442372 bytes allocated	works, no reset

Normal boot with PSRAM available is unchanged. Fork CI green on this branch.