tests/bit_operations_tests: bit-shifts with negative RHSes are undefined behavior

[nwf]

The bit_operations_tests probe at the behavior of 1U << -1 within the loop at

spandsp/tests/bit_operations_tests.c

Lines 291 to 293 in 7977601

	for (i = -1; i < 32; i++)
	{
	ax32 = most_significant_one32(1U << i);

This is, formally, undefined behavior in C. Specifically, C23 §6.5.8 ¶3 says "If the value of the right operand is negative or [...], the behavior is undefined." I think that the loop variable should start at 0 and, if the behavior of most_significant_one32 on 0 is to be tested, specific code should be added. Does that seem reasonable?