Ensure delays of the origin image is preserved

[kleisauke]

By not initializing the delay vector, since we assume it's empty by default in SetAnimationProperties.

sharp/src/common.cc

Lines 495 to 503 in 68823a5

	bool hasDelay = !delay.empty();
	// Avoid a copy if none of the animation properties are needed.
	if (nPages == 1 && !hasDelay && loop == -1) return image;
	if (delay.size() == 1) {
	// We have just one delay, repeat that value for all frames.
	delay.insert(delay.end(), nPages - 1, delay[0]);
	}

A test case was added to prevent further regressions.

See: #3061.

[coveralls]

Coverage remained the same at 100.0% when pulling 1f09d28 on kleisauke:preserve-origin-delays into 68823a5 on lovell:main.

[lovell]

Bedankt!