I consider this an interim workaround/hack until #1299 is finished.
There is a bug in the original C implementation of the errol3 (and errol4)
algorithm that can result in undefined behavior or an obviously incorrect
result (leading ':' in the output)
This change checks for those two problems and uses a slower fallback
path if they occur. I can't guarantee that this will always produce
the correct result, but since the workaround is only used if the original
algorithm is guaranteed to fail, it should never turn a previously-correct
result into an incorrect one.
Fixes#11283
b4bf3bdf7e